This document provides an introduction to backlinks and their importance for search engine optimization. It defines backlinks as incoming links to a website and notes that Google's original search algorithm, BackRub, analyzed backlinks to determine a site's importance. The author emphasizes that backlinks remain a major factor in Google's ranking system, with more and higher-quality backlinks from relevant sites helping to increase a website's visibility and traffic. The remainder of the document provides various methods for finding backlink opportunities.