An Affiliate in a broad sense is any online site which wishes to partner with the Expedia brand, products and services. By joining the Expedia affiliate program you get the opportunity to team up with a number of online travel agencies, to earn additional revenue. Leverage the Expedia brand to better serve your visitors and to attract new people by featuring links on your site for promotions, and inventory. Wherein Expedia's merchant API enables a single buyer to pay multiple merchants in a single checkout.