Affiliate marketing is a method of promoting web businesses in which an affiliate is rewarded for every visitor, subscriber, customer, and/or sale provided through his/her efforts. It is a modern variation of the practice of paying a finder's fee for the introduction of new clients to a business. Compensation may be made based on a certain value for each visit (Pay per click), registrant (Pay per lead), or a commission for each customer or sale (Pay per sale), or any combination.

Merchants like affiliate marketing because it is a "pay for performance model", meaning the merchant does not incur a marketing expense unless results are realized.

Some e-commerce sites run their own affiliate programs while other e-commerce vendors use third party services provided by intermediaries to track traffic or sales that are referred from affiliates. Some businesses owe much of their growth and success to this marketing technique, especially small and midsize businesses.

Merchants who are considering adding an affiliate strategy to their online sales channel have different technological solutions available to them. Some types of affiliate management solutions include: standalone software, hosted services, shopping carts with affiliate features, and third party affiliate networks.

Revenue generated online grew quickly. The e-commerce website, viewed as a marketing toy in the early days of the web, became an integrated part of the overall business plan and in some cases grew to a bigger business than the existing offline business. Many companies hired outside affiliate management companies to manage the affiliate program (see outsourced program management.

According to one report, total sales generated through affiliate networks in 2006 was £2.16 billion in the UK alone. The estimates were £1.35 billion in sales in 2005. [1] MarketingSherpa's research team roughly estimates affiliates worldwide will earn $6.5 billion in bounty and commissions in 2006. This includes retail, personal finance, gaming and gambling, travel, telecom, 'Net marketing' education offers, subscription sites, and other lead generation, but it does not include contextual ad networks such as Google AdSense. [2]

Currently the most active sectors for affiliate marketing are the adult, gambling and retail sectors. The three sectors expected to experience the greatest growth in affiliate marketing are the mobile phone, finance and travel sectors. A lot of different offers from various Advertisers are available to pick from. Hot on the heels of these are the entertainment (particularly gaming) and internet-related services (particularly broadband) sectors. Also several of the affiliate solution providers expect to see increased interest from B2B marketers and advertisers in using affiliate marketing as part of their mix. Of course, this is constantly subject to change.