1. Introduction

In the old days of the world wide web, you could only find pages by following links from one to another. These days, though, there are billions of individual websites with countless web pages. Better tools are needed for internet users to find the information that they are looking for.

Search engines are the solution. There are now many different search engines, each using their own technologies and algorithms to index web pages across the world wide web. Google is by far the most popular, but others include Bing, Yahoo, and DuckDuckGo.

This section describes some of the technology behind these essential services, including

• Crawlers
• Page ranking