Search engine marketing (SEM) involves promoting websites to increase visibility in search engine results pages through optimization and advertising. SEM uses search engine optimization (SEO) which adjusts website content for higher search rankings, or pay per click (PPC) listings. SEM covers activities like SEO, managing paid listings, and developing online marketing strategies. As the number of websites grew in the 1990s, search engines and pay per click programs from companies like Open Text and Goto.com emerged to help people find information. Google later introduced AdWords in 2000. By 2007, PPC programs became primary revenue sources for search engines. SEM consultants and agencies emerged to help businesses use search engine advertising opportunities.