Sources such as encyclopedias, handbooks, or other books can offer an overview of your topic, providing critical background information needed for you to set the stage for your audience, the reader.
These types of sources will typically be a in literature review format, documenting the key concepts you'll need to know, and providing core references to other sources that may be useful for you to draw from in your paper.
Many encyclopedias and handbooks can be found on the Psychology Reference Sources guide, with some relating specifically to psychological disorders listed below.
APA Handbook of Psychopathology, Vol. 1: Psychopathology: Understanding, Assessing, and Treating Adult Mental Disorders by APA Handbook of Psychopathology, Vol. 2: Psychopathology in Children and Adolescents by Other books found through the library discovery system may have a chapter on a concept in which you're interested.
Search Library Resources from the library's home page to discover books.
When searching in APA PsycInfo later for articles, also take a look at the abstracts there for book chapters, and return to this initial search for books as needed.
Below are examples of the types of books that may be useful:
Clinical Handbook of Psychological Disorders, Sixth Edition by 
Treatment of Disorders in Childhood and Adolescence, Fourth Edition by 
