Dictionaries and encyclopedias are great reference tools, because they can help you identify key information about a musician, musical topic, genre, style, etc. fairly quickly.
Encyclopedias, such as The New Grove Dictionary of Music and Musicians, feature entries for musical terms, topics, or people. Entries for musicians are particularly useful because they will include a list of works (some more comprehensive than others), bibliographies for further research and related sources.
Keep in mind that print reference tools will go out of date and may not include information about contemporary/emerging people, topics, or issues in music. Online reference tools are available (see below) for several of the more exhaustive dictionary and encyclopedia titles.