The latest edition of the APA's Diagnostic & Statistical Manual of Mental Disorders, the DSM 5 is available online and in print. The previous edition, the DSM 5-TR, is available only in print.
Copies of the Publication Manual of the American Psychological Association, the authoritative source for APA style, are available on the library shelves.
For quick access, see Gelman REFERENCE 2nd floor. The call number is BF76.7 .P83 2010
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Purdue's OWL site covers the most common types of citation in APA.