Pay per click (PPC) is an Internet advertising model employed on search engines, advertising networks and content websites, where advertisers only pay when a user really clicks on an advertisement to visit the advertisers' website. With search engines, advertisers usually bid on keyword phrases relevant to their target market.

Though many PPC providers exist, but Google AdWords, Yahoo Search Marketing and Microsoft ad Center are the largest network operators as of 2007. The PPC advertising model is open to maltreatment through click fraud, although Google and other search engines have employed automated systems to guard against abusive clicks by competitors or corrupt webmasters.