This document provides an introduction to search engine optimization (SEO). It explains that SEO is the process of improving website traffic from organic search results. It describes how search engines work by crawling websites, indexing pages, calculating relevancy, and serving results. Key on-page and off-page ranking factors are identified that search engines use to determine relevance and importance, including keywords, content, links, and social signals. Both white hat and black hat SEO techniques are discussed. The importance of SEO for driving qualified traffic to a website is emphasized.