Search engine marketing (SEM) is Internet marketing that promotes websites in search engine result pages (SERPs). When a company uses SEM to find prospects, it is typically buying paid search listings through Google AdWords, Yahoo Search Marketing and Microsoft adCenter. In 2006, American advertisers spent $9.4 billion on search engine marketing. SEM is the fastest growing form of advertising for 2 simple reasons. It is affordable for businesses small and large, and it works!