Affiliate Networks are specialized advertising vendors that broker transactions between brands/advertisers and publishers (affiliates). Publishers are generally allowed to join Affiliate Networks at no cost. Brands pay a fee to participate in the network in exchange for making use of the network's advanced tracking and reporting tools, simplified payment processing, and access to a larger base of affiliates/publishers that they would otherwise be unable to reach. A standard set of cost models guides the transactional relationship, typically either revenue sharing, performance-based or Cost-per-Impression (CPM) depending upon the terms of the affiliate program.