An affiliate network acts as an intermediary between publishers (affiliates) and merchant affiliate programs. It allows website publishers to more easily find and participate in affiliate programs which are suitable for their website (and thus generate income from those programs), and allows websites offering affiliate programs (typically online merchants) to reach a larger audience by promoting their affiliate programs to all of the publishers participating in the affiliate network.

Traditional affiliate networks enable merchants to offer publishers a share of any revenue that is generated by the merchant from visitors to the publisher's site, or a fee for each visitor on the publisher's site that completes a specific action (making a purchase, registering for a newsletter, etc.). The majority of merchant programs have a revenue share model, as opposed to a fee-per-action model.

For merchants, affiliate network services and benefits may include tracking technology, reporting tools, payment processing, and access to a large base of publishers. For affiliates, services and benefits can include simplifying the process of registering for one or more merchant affiliate programs, reporting tools, and payment aggregation.

Affiliates are generally able to join affiliate networks for free, whereas there is generally a fee for merchants to participate. Traditional affiliate networks might charge an initial setup fee and/or a recurring membership fee. It is also common for affiliate networks to charge merchants a percentage of the commissions paid to affiliates.

The first affiliate network in the UK was Deal Group Media, based in Camden, North London, in 1999. As of April 2010 there are now 10 major UK-based operators in the field.