The rules for citing online sources can be found in Bluebook Rule 18 with General Internet Citation Principles found in Rule 18.2.1. These principles encourage citing online sources like print sources when possible but call for appending a URL to the end of a citation when doing so would "substantially improve access to the source cited" or when "an online source shares the characteristics of a print source such that it could be fully cited according to another rule." The principles also recommend including an archival link using a reliable tool, such as the Internet Archive's Wayback Machine or Perma.cc, or by saving the source as a PDF and storing it on file.
A common issue in creating citations for internet sources is determining which titles to include. Rule 18.2.2(b) provides rules and examples for citing to headings, main page titles, titles for subdivisions of a larger source, and descriptive sources. These categories may not correspond directly to the layout of a particular website, but can be used as a starting point.
The Bluebook provides different rules for citing particular types of sources from what it calls "commercial electronic databases," which it primarily uses to mean Lexis, Westlaw, and Bloomberg Law. Rule 18.4 collects all the other rules in the Bluebook that provide specific citation formats for materials from these databases.
The Internet Archive's Wayback Machine is a service that allows users to look at archived versions of webpages. The Wayback Machine is helpful for looking at previous versions of webpages and can be used to track down links that no longer work properly. The Wayback Machine can also be used to create an archival link to add to a citation.