This document provides an introduction to search engine optimization (SEO). It defines search engines and how they work by using spiders to crawl the web, index content in databases, and rank documents using algorithms. The document then defines SEO as the process of improving websites to achieve higher search engine rankings. It explains why SEO is important by noting that most traffic comes from search engines and users rarely view results past the first page. The document outlines the SEO process, including assessment, planning, execution and maintenance. It also covers on-page and off-page SEO techniques.