Search engine optimization (SEO) is actually a component of search engine marketing—a function of the SEM process, if you will. SEO is the act of optimizing a website for organic or natural search engine listings. Search engine optimization is arguably the most cost-effective function in a search engine marketing campaign, yet still just one element.

Search engine marketing (SEM) is the process of marketing a website via Internet search engines; whether by improving rank in organic or natural listings, paid or sponsored listings or a combination thereof.