7 Best Affiliate Marketing Programs to Join in 2024

Expert

3 Feb, 2024

Affiliate Marketing Programs

Affiliate marketing is one of the most popular and profitable ways to make money online. It is a type of performance-based marketing where you earn a commission for promoting other people's or companies' products or services on your website, blog, social media, or email list.

By joining affiliate marketing programs, you can leverage the power and influence of established brands and products, and offer value and solutions to your audience. You can also earn passive income by generating sales or leads for the merchants, without having to create your own products, handle inventory, shipping, or customer service.

However, not all affiliate marketing programs are created equal. Some offer higher commissions, better support, more flexibility, and more opportunities than others. Some are more suitable for your niche, audience, and goals than others. Some are more trustworthy, reliable, and reputable than others.

So, how do you choose the best affiliate marketing programs to join in 2024? In this article, we will review and compare 7 of the best affiliate marketing programs that you can join in 2024. We will look at their
features, benefits, drawbacks, and requirements. We will also provide some tips and best practices on how to succeed with affiliate marketing in 2024.

This article is divided into the following sections:

Summary with hyperlinks
Introduction
Health and Wellness
Personal Finance
E-commerce and Dropshipping
Technology and Gadgets
Travel and Adventure
Food and Cooking
Education and Learning
Conclusion
FAQs

Summary with hyperlinks

This format provides an overview of the main points and allows the reader to navigate to the sections that interest them. Here are the 7 best affiliate marketing programs to join in 2024:

Category	Subcategory	Affiliate Program	Commission Rate	Cookie Duration
Health and Wellness	Fitness	Bodybuilding.com	15%	9 days
Health and Wellness	Nutrition	Vital Proteins	10%	30 days
Personal Finance	Investing	Acorns	$5 per referral	45 days
Personal Finance	Insurance	Policygenius	$50-$100 per lead	30 days
E-commerce and Dropshipping	Online Store Builder	Shopify	200% of the first month's subscription fee	30 days
E-commerce and Dropshipping	Dropshipping Platform	Spocket	20-30% recurring commission	30 days
Technology and Gadgets	Web Hosting	Bluehost	$65-$130 per sale	90 days
Technology and Gadgets	Software	Adobe	85% of the first month's subscription fee	30 days
Travel and Adventure	Booking Platform	Booking.com	25-40% of the commission received by Booking.com	Session-based
Travel and Adventure	Travel Gear	REI	5%	30 days
Food and Cooking	Meal Delivery Service	HelloFresh	$10-$20 per sale	14 days
Food and Cooking	Cookware	Le Creuset	5%	30 days
Education and Learning	Online Courses	Udemy	15%	7 days
Education and Learning	Language Learning	Babbel	$10-$20 per sale	30 days

Introduction

So, how do you choose the best affiliate marketing programs to join in 2024? In this article, we will review and compare 7 of the best affiliate marketing programs that you can join in 2024. We will look at their features, benefits, drawbacks, and requirements. We will also provide some tips and best practices on how to succeed with affiliate marketing in 2024.

Let's get started!

Health and Wellness

The health and wellness niche is one of the most evergreen and profitable niches in affiliate marketing. People are always looking for ways to improve their physical and mental health, fitness, nutrition, and well-being. The global health and wellness market is expected to reach $6.5 trillion by 2025, according to Statista.

If you have a website, blog, social media, or email list that focuses on health and wellness topics, such as weight loss, fitness, yoga, meditation, nutrition, supplements, skincare, etc., you can join some of the best affiliate marketing programs in this niche and earn a healthy income.

Here are two of the best affiliate marketing programs in the health and wellness niche that you can join in 2024:

Bodybuilding.com

Bodybuilding.com is the world's largest online fitness store and community. It offers a wide range of products, such as supplements, clothing, equipment, accessories, and more. It also provides a lot of valuable content, such as articles, videos, podcasts, forums, and programs, to help people achieve their fitness goals.

By joining the Bodybuilding.com affiliate program, you can promote their products and content to your audience and earn a 15% commission on every sale. You can also earn a 5% commission on every sale made by the affiliates that you refer to the program. You will have access to a dedicated affiliate manager, exclusive offers, banners, links, and tracking tools.

The Bodybuilding.com affiliate program is managed by Impact Radius. You can join the program by filling out an online application form and waiting for approval. The cookie duration is 9 days, which means you will earn a commission if the customer makes a purchase within 9 days of clicking on your affiliate link.

The Bodybuilding.com affiliate program is ideal for affiliates who have a fitness-related website, blog, social media, or email list. You can offer your audience a variety of products and content that can help them improve their fitness and health.

Vital Proteins

Vital Proteins is a leading brand of collagen products, such as powders, capsules, gummies, creams, and more. Collagen is a protein that supports the health of the skin, hair, nails, joints, bones, and muscles. Vital Proteins products are made from high-quality ingredients, such as grass-fed, pasture-raised bovine, wild-caught fish, and organic fruits and vegetables.

By joining the Vital Proteins affiliate program, you can promote their products to your audience and earn a 10% commission on every sale. You will also receive a 10% discount code that you can share with your audience. You will have access to a dedicated affiliate manager, exclusive offers, banners, links, and tracking tools.

The Vital Proteins affiliate program is managed by ShareASale. You can join the program by signing up for a free ShareASale account and applying for the Vital Proteins affiliate program. The cookie duration is 30 days, which means you will earn a commission if the customer makes a purchase within 30 days of clicking on your affiliate link.

The Vital Proteins affiliate program is ideal for affiliates who have a health and wellness-related website, blog, social media, or email list. You can offer your audience a range of products that can help them boost their collagen intake and improve their health and beauty.

Personal Finance

The personal finance niche is another evergreen and profitable niche in affiliate marketing. People are always looking for ways to manage their money, save, invest, budget, pay off debt, and achieve financial freedom. The global personal finance software market is expected to reach $1.57 billion by 2025, according to Grand View Research.

If you have a website, blog, social media, or email list that focuses on personal finance topics, such as investing, banking, insurance, credit cards, loans, taxes, etc., you can join some of the best affiliate marketing programs in this niche and earn a lucrative income.

Here are two of the best affiliate marketing programs in the personal finance niche that you can join in 2024:

Acorns

Acorns is a popular app that helps people save and invest their spare change. It automatically rounds up the purchases made with a linked debit or credit card and invests the difference in a diversified portfolio of ETFs. It also offers other features, such as retirement accounts, checking accounts, debit cards, cash back, and more.

By joining the Acorns affiliate program, you can promote their app to your audience and earn $5 for every referral who signs up and makes their first investment. You can also earn bonuses and incentives for reaching certain milestones. You will have access to a dedicated affiliate manager, exclusive offers, banners, links, and tracking tools.

The Acorns affiliate program is managed by FlexOffers. You can join the program by signing up for a free FlexOffers account and applying for the Acorns affiliate program. The cookie duration is 45 days, which means you will earn a commission if the customer signs up and makes their first investment within 45 days of clicking on your affiliate link.

People also read: How to Make Money with Affiliate Marketing in 2024

The Acorns affiliate program is ideal for affiliates who have a personal finance-related website, blog, social media, or email list. You can offer your audience a simple and convenient way to save and invest their money and grow their wealth.

Policygenius

Policygenius is a leading online platform that helps people compare and buy insurance policies, such as life, home, auto, renters, pet, disability, and more. It offers unbiased and transparent advice, personalized quotes, and hassle-free applications from over 30 top-rated insurers.

By joining the Policygenius affiliate program, you can promote their platform to your audience and earn $50-$100 for every qualified lead. A qualified lead is someone who completes an online application for a life, home, or auto insurance policy. You will have access to a dedicated affiliate manager, exclusive offers, banners, links, and tracking tools.

The Policygenius affiliate program is managed by CJ Affiliate. You can join the program by signing up for a free CJ Affiliate account and applying for the Policygenius affiliate program. The cookie duration is 30 days, which means you will earn a commission if the customer completes an online application within 30 days of clicking on your affiliate link.

The Policygenius affiliate program is ideal for affiliates who have a personal finance-related website, blog, social media, or email list. You can offer your audience a smart and easy way to compare and buy insurance policies and protect their financial future.

E-commerce and Dropshipping

The e-commerce and dropshipping niche is one of the most booming and profitable niches in affiliate marketing. People are always looking for ways to start and grow their own online businesses, sell products online, and make money from home. The global e-commerce market is expected to reach $6.54 trillion by 2022, according to Statista.

If you have a website, blog, social media, or email list that focuses on e-commerce and dropshipping topics, such as online store builders, dropshipping platforms, product sourcing, marketing, branding, etc., you can join some of the best affiliate marketing programs in this niche and earn a generous income.

Here are two of the best affiliate marketing programs in the e-commerce and dropshipping niche that you can join in 2024:

Shopify

Shopify is the world's leading online store builder and e-commerce platform. It allows anyone to create and run their own online store, sell products online, and manage their business. It offers a range of features, such as themes, apps, domains, hosting, payments, shipping, marketing, analytics, and more.

By joining the Shopify affiliate program, you can promote their platform to your audience and earn 200% of the first month's subscription fee for every customer who signs up for a paid plan. You can also earn 20% of the Shopify app or theme revenue for every customer who purchases an app or theme through your affiliate link. You will have access to a dedicated affiliate manager, exclusive offers, banners, links, and tracking tools.

The Shopify affiliate program is managed by Shopify. You can join the program by filling out an online application form and waiting for approval. The cookie duration is 30 days, which means you will earn a commission if the customer signs up for a paid plan within 30 days of clicking on your affiliate link.

The Shopify affiliate program is ideal for affiliates who have an e-commerce and dropshipping-related website, blog, social media, or email list. You can offer your audience a powerful and user-friendly platform to create and grow their own online store and sell products online.

Spocket

Spocket is a leading dropshipping platform that connects online sellers with thousands of verified suppliers from around the world. It allows sellers to find and import high-quality products to their online store, set their own prices and margins, and fulfill orders with one click. It also offers features such as inventory management, order tracking, branded invoicing, and more.

By joining the Spocket affiliate program, you can promote their platform to your audience and earn 20-30% recurring commission for every customer who signs up for a paid plan. You can also earn bonuses and incentives for reaching certain milestones. You will have access to a dedicated affiliate manager, exclusive offers, banners, links, and tracking tools.

The Spocket affiliate program is managed by PartnerStack. You can join the program by signing up for a free PartnerStack account and applying for the Spocket affiliate program. The cookie duration is 30 days, which means you will earn a commission if the customer signs up for a paid plan within 30 days of clicking on your affiliate link.

The Spocket affiliate program is ideal for affiliates who have an e-commerce and dropshipping-related website, blog, social media, or email list. You can offer your audience a reliable and convenient way to find and sell products online without having to deal with inventory, shipping, or logistics.

Technology and Gadgets

The technology and gadgets niche is one of the most dynamic and profitable niches in affiliate marketing. People are always looking for ways to improve their productivity, entertainment, communication, and security with the latest and greatest technology and gadgets. The global consumer electronics market is expected to reach $1.97 trillion by 2024, according to Zion Market Research.

If you have a website, blog, social media, or email list that focuses on technology and gadgets topics, such as web hosting, software, hardware, gaming, mobile, smart home, etc., you can join some of the best affiliate marketing programs in this niche and earn a handsome income.

Here are two of the best affiliate marketing programs in the technology and gadgets niche that you can join in 2024:

Bluehost

Bluehost is one of the most popular and reliable web hosting providers in the world. It offers a range of web hosting services, such as shared, VPS, dedicated, WordPress, and WooCommerce hosting. It also offers features such as domains, SSL certificates, email accounts, backups, security, and more.

By joining the Bluehost affiliate program, you can promote their web hosting services to your audience and earn $65-$130 per sale. You can also earn bonuses and incentives for reaching certain milestones. You will have access to a dedicated affiliate manager, exclusive offers, banners, links, and tracking tools.

The Bluehost affiliate program is managed by Bluehost. You can join the program by filling out an online application form and waiting for approval. The cookie duration is 90 days, which means you will earn a commission if the customer makes a purchase within 90 days of clicking on your affiliate link.

The Bluehost affiliate program is ideal for affiliates who have a technology and gadgets-related website, blog, social media, or email list. You can offer your audience a fast and secure web hosting service that can help them create and grow their own online presence.

Adobe

Adobe is a leading software company that offers a range of creative and digital solutions, such as Photoshop, Illustrator, Premiere Pro, Acrobat, Lightroom, and more. It also offers cloud-based platforms, such as Creative Cloud, Document Cloud, and Experience Cloud, that allow users to access, edit, and share their work from anywhere.

By joining the Adobe affiliate program, you can promote their software and cloud services to your audience and earn 85% of the first month's subscription fee for every customer who signs up for a monthly plan, or 8.33% of the first year's subscription fee for every customer who signs up for an annual plan. You will have access to a dedicated affiliate manager, exclusive offers, banners, links, and tracking tools.

The Adobe affiliate program is managed by Awin. You can join the program by signing up for a free Awin account and applying for the Adobe affiliate program. The cookie duration is 30 days, which means you will earn a commission if the customer signs up for a plan within 30 days of clicking on your affiliate link.

The Adobe affiliate program is ideal for affiliates who have a technology and gadgets-related website, blog, social media, or email list. You can offer your audience a range of software and cloud services that can help them unleash their creativity and digital potential.

Travel and Adventure

The travel and adventure niche is one of the most exciting and profitable niches in affiliate marketing. People are always looking for ways to explore new destinations, experience different cultures, and enjoy various activities. The global travel and tourism market is expected to reach $11.4 trillion by 2025, according to Allied Market Research.

If you have a website, blog, social media, or email list that focuses on travel and adventure topics, such as booking platforms, travel gear, travel guides, travel photography, etc., you can join some of the best affiliate marketing programs in this niche and earn a rewarding income.

Here are two of the best affiliate marketing programs in the travel and adventure niche that you can join in 2024:

Booking.com

Booking.com is the world's leading online travel agency that offers a wide range of travel services, such as hotels, flights, car rentals, tours, attractions, and more. It has over 28 million listings in over 220 countries and territories. It also offers features such as free cancellation, price match, customer reviews, and more.

By joining the Booking.com affiliate program, you can promote their travel services to your audience and earn 25-40% of the commission received by Booking.com for every confirmed booking. You will have access to a dedicated affiliate manager, exclusive offers, banners, links, and tracking tools.

The Booking.com affiliate program is managed by Booking.com. You can join the program by filling out an online application form and waiting for approval. The cookie duration is session-based, which means you will earn a commission if the customer makes a booking within the same browser session of clicking on your affiliate link.

The Booking.com affiliate program is ideal for affiliates who have a travel and adventure-related website, blog, social media, or email list. You can offer your audience a comprehensive and convenient platform to book their travel needs and enjoy their trips.

REI

REI is a leading outdoor retailer that offers a wide range of products, such as clothing, footwear, equipment, accessories, and more. It also offers services such as classes, events, rentals, adventures, and more. It caters to various outdoor activities, such as hiking, camping, cycling, climbing, skiing, kayaking, and more.

By joining the REI affiliate program, you can promote their products and services to your audience and earn a 5% commission on every sale. You will also receive a 10% discount code that you can share with your audience. You will have access to a dedicated affiliate manager, exclusive offers, banners, links, and tracking tools.

The REI affiliate program is managed by AvantLink. You can join the program by signing up for a free AvantLink account and applying for the REI affiliate program. The cookie duration is 30 days, which means you will earn a commission if the customer makes a purchase within 30 days of clicking on your affiliate link.

The REI affiliate program is ideal for affiliates who have a travel and adventure-related website, blog, social media, or email list. You can offer your audience a variety of products and services that can help them enjoy their outdoor activities and adventures.

Food and Cooking

The food and cooking niche is one of the most delicious and profitable niches in affiliate marketing. People are always looking for ways to satisfy their taste buds, improve their culinary skills, and enjoy different cuisines. The global food and beverage market is expected to reach $7.5 trillion by 2023, according to Research and Markets.

If you have a website, blog, social media, or email list that focuses on food and cooking topics, such as recipes, meal delivery services, cookware, kitchen gadgets, etc., you can join some of the best affiliate marketing programs in this niche and earn a tasty income.

Here are two of the best affiliate marketing programs in the food and cooking niche that you can join in 2024:

HelloFresh

HelloFresh is a popular meal delivery service that delivers fresh and pre-portioned ingredients and easy-to-follow recipes to your door. It allows you to choose from a variety of menus, such as classic, veggie, family, low-calorie, etc., and customize your delivery frequency, servings, and preferences. It also offers features such as gift cards, wine club, and more.

By joining the HelloFresh affiliate program, you can promote their meal delivery service to your audience and earn $10-$20 per sale. You will also receive a $80 discount code that you can share with your audience. You will have access to a dedicated affiliate manager, exclusive offers, banners, links, and tracking tools.

The HelloFresh affiliate program is managed by Awin. You can join the program by signing up for a free Awin account and applying for the HelloFresh affiliate program. The cookie duration is 14 days, which means you will earn a commission if the customer makes a purchase within 14 days of clicking on your affiliate link.

The HelloFresh affiliate program is ideal for affiliates who have a food and cooking-related website, blog, social media, or email list. You can offer your audience a convenient and healthy way to cook delicious meals at home and save time and money.

Le Creuset

Le Creuset is a premium brand of cookware, bakeware, kitchenware, and accessories. It is famous for its colorful and durable cast iron products, such as pots, pans, casseroles, skillets, etc. It also offers products made from stainless steel, stoneware, silicone, and more. It caters to various cooking styles, such as roasting, baking, grilling, frying, and more.

By joining the Le Creuset affiliate program, you can promote their products to your audience and earn a 5% commission on every sale. You will also receive a 10% discount code that you can share with your audience. You will have access to a dedicated affiliate manager, exclusive offers, banners, links, and tracking tools.

The Le Creuset affiliate program is managed by Rakuten. You can join the program by signing up for a free Rakuten account and applying for the Le Creuset affiliate program. The cookie duration is 30 days, which means you will earn a commission if the customer makes a purchase within 30 days of clicking on your affiliate link.

The Le Creuset affiliate program is ideal for affiliates who have a food and cooking-related website, blog, social media, or email list. You can offer your audience a range of products that can help them cook and serve their food with style and quality.

Education and Learning

The education and learning niche is one of the most rewarding and profitable niches in affiliate marketing. People are always looking for ways to learn new skills, acquire new knowledge, and advance their careers. The global online education market is expected to reach $319.16 billion by 2025, according to Research and Markets.

If you have a website, blog, social media, or email list that focuses on education and learning topics, such as online courses, language learning, certifications, degrees, etc., you can join some of the best affiliate marketing programs in this niche and earn a generous income.

Here are two of the best affiliate marketing programs in the education and learning niche that you can join in 2024:

Udemy

Udemy is the world's largest online learning platform that offers over 150,000 courses in various topics, such as business, design, development, marketing, photography, music, and more. It allows anyone to learn from expert instructors, access on-demand video lectures, quizzes, assignments, and certificates, and join a community of over 40 million learners.

By joining the Udemy affiliate program, you can promote their courses to your audience and earn a 15% commission on every sale. You will have access to a dedicated affiliate manager, exclusive offers, banners, links, and tracking tools.

The Udemy affiliate program is managed by Rakuten. You can join the program by signing up for a free Rakuten account and applying for the Udemy affiliate program. The cookie duration is 7 days, which means you will earn a commission if the customer makes a purchase within 7 days of clicking on your affiliate link.

The Udemy affiliate program is ideal for affiliates who have an education and learning-related website, blog, social media, or email list. You can offer your audience a wide range of courses that can help them learn new skills, acquire new knowledge, and advance their careers.

Babbel

Babbel is a popular language learning app that offers 14 languages, such as Spanish, French, German, Italian, and more. It allows users to learn from interactive lessons, speech recognition, vocabulary trainers, and real-life scenarios. It also offers features such as progress tracking, personalized review, and offline mode.

By joining the Babbel affiliate program, you can promote their app to your audience and earn $10-$20 per sale. You will also receive a 25% discount code that you can share with your audience. You will have access to a dedicated affiliate manager, exclusive offers, banners, links, and tracking tools.

The Babbel affiliate program is managed by CJ Affiliate. You can join the program by signing up for a free CJ Affiliate account and applying for the Babbel affiliate program. The cookie duration is 30 days, which means you will earn a commission if the customer makes a purchase within 30 days of clicking on your affiliate link.

The Babbel affiliate program is ideal for affiliates who have an education and learning-related website, blog, social media, or email list. You can offer your audience a fun and effective way to learn a new language and communicate with confidence.

Conclusion

In this article, we have reviewed and compared 7 of the best affiliate marketing programs that you can join in 2024. We have looked at their features, benefits, drawbacks, and requirements. We have also provided some tips and best practices on how to succeed with affiliate marketing in 2024.

Here are the main takeaways from this article:

Affiliate marketing is a type of performance-based marketing where you earn a commission for promoting other people's or companies' products or services on your website, blog, social media, or email list.
Affiliate marketing is a great way to make money online, as you can leverage the power and influence of established brands and products, offer value and solutions to your audience, and earn passive income by generating sales or leads for the merchants.
However, not all affiliate marketing programs are created equal. Some offer higher commissions, better support, more flexibility, and more opportunities than others. Some are more suitable for your niche, audience, and goals than others. Some are more trustworthy, reliable, and reputable than others.
Therefore, you need to choose the best affiliate marketing programs to join in 2024, based on your niche, audience, and goals. You also need to follow some tips and best practices to succeed with affiliate marketing in 2024, such as creating high-quality and engaging content, using keywords and SEO techniques, building trust and credibility, tracking and optimizing your performance, and updating your content regularly.

FAQs

In this section, we will answer some of the most frequently asked questions about affiliate marketing. We will use the HTML element

to create a collapsible section of content on the web page.

Which program is best for affiliate marketing?

There is no definitive answer to this question, as the best program for affiliate marketing depends on your niche, audience, and goals. However, some general criteria that you can use to evaluate and compare different programs are:

The commission rate: how much you earn for each sale or lead.
The cookie duration: how long you have to earn a commission after the customer clicks on your affiliate link.
The product or service quality: how good, useful, and relevant the product or service is for your audience.
The support and resources: how much help and guidance you get from the merchant and the network.
The reputation and trustworthiness: how reliable and reputable the merchant and the network are.

Based on these criteria, you can choose the best program for affiliate marketing that suits your niche, audience, and goals.

What is the highest paid affiliate program?

Again, there is no definitive answer to this question, as the highest paid affiliate program depends on various factors, such as the commission rate, the average order value, the conversion rate, the competition, and the demand. However, some general niches that tend to have higher paid affiliate programs are:

Personal finance: such as investing, banking, insurance, credit cards, loans, etc.
Technology and gadgets: such as web hosting, software, hardware, gaming, mobile, smart home, etc.
E-commerce and dropshipping: such as online store builders, dropshipping platforms, product sourcing, marketing, branding, etc.
Health and wellness: such as fitness, nutrition, supplements, skincare, etc.
Education and learning: such as online courses, language learning, certifications, degrees, etc.

Based on these niches, you can find the highest paid affiliate program that matches your niche, audience, and goals.

How do beginners get into affiliate marketing?

Affiliate marketing is not a get-rich-quick scheme, but a legitimate and rewarding way to make money online. However, it does require some time, effort, and skills to get started and succeed. Here are some steps that beginners can follow to get into affiliate marketing:

Choose a niche: a specific topic or category that you are passionate and knowledgeable about, and that has a large and profitable market.
Build a platform: a website, blog, social media, or email list that you can use to create and share content, attract and engage your audience, and promote your affiliate offers.
Join an affiliate program: a program that offers products or services that are relevant and valuable to your niche and audience, and that pays you a commission for each sale or lead that you generate.
Create content: high-quality and engaging content that provides information, solutions, and recommendations to your audience, and that includes your affiliate links or banners.
Drive traffic: methods and strategies that you can use to attract and direct visitors to your platform, such as SEO, social media, email marketing, paid ads, etc.
Convert and earn: techniques and tools that you can use to persuade and encourage your visitors to click on your affiliate links or banners, and make a purchase or take an action, such as landing pages, calls to action, testimonials, reviews, etc.

By following these steps, beginners can get into affiliate marketing and start making money online.

What is the easiest affiliate program to make money?

There is no easy affiliate program to make money, as every program has its own advantages and disadvantages, and requires some work and skills to succeed. However, some general factors that can make an affiliate program easier to make money are:

The product or service demand: how popular and sought-after the product or service is among your audience and the market.
The product or service quality: how good, useful, and relevant the product or service is for your audience and their needs.
The commission rate: how much you earn for each sale or lead.
The cookie duration: how long you have to earn a commission after the customer clicks on your affiliate link.
The support and resources: how much help and guidance you get from the merchant and the network.

Based on these factors, you can find the easiest affiliate program to make money that fits your niche, audience, and goals.

7 Best Affiliate Marketing Programs to Join in 2024

Summary with hyperlinks

Introduction