搜索引擎行销(Search Engine Marketing) 或缩写SEM，是一种以透过增加搜索引擎结果页(Search Engine Result Pages, SERPs)能见度的方式，或是透过搜索引擎的内容联播网来推销网站的网络行销模式。

根据搜索引擎行销专业机构(Search Engine Marketing Professionals Organization, SEMPO)整理出目前主流的SEM包含：搜索引擎最佳化(SEO)、关键字点击广告(PPC)及付费收录广告(PFI)。

而纽约时报定义 SEM 是一种透过购买搜索列表以达成比免费列表更高排名目标的手段

Search engine marketing (SEM) is a form of Internet marketing that involves the promotion of websites by increasing their visibility in search engine results pages (SERPs) primarily through paid advertising. SEM may incorporate search engine optimization (SEO), which adjusts or rewrites website content and site architecture to achieve a higher ranking in search engine results pages to enhance pay per click (PPC) listings.