Bluebook Rule (20th): 18
In general, the Bluebook requires citation to traditional printed sources when available. However, in several instances, the Bluebook permits citation to the digital copy, either directly or as a parallel citation.
General Rules for citing electronic documents
Below are some general guidelines for citing electronic media in Bluebook format:
Bluebook Rule (20th): 18.2.1
The Bluebook states that if you have an authenticated or official digital copy, or a digital copy that is an exact copy of the source, you can cite to it as if it were the original print source. If the cited source is available in print but practically unavailable, you should cite as if to the printed source, but include the URL at the end of the citation.
Direct Citations to Internet Sources
Bluebook Rule (20th): 18.2.2
Citation to commercial electronic databases
Bluebook Rule (20th): 18.3