The NCBI Bookshelf is a collection of over 150 online textbooks and biomedical books made available in collaboration with authors and publishers. As a separate Entrez database, the content of the Bookshelf can be searched using text queries or can be found through links from other Entrez databases, particularly PubMed, PMC, Gene and Online Mendelian Inheritance in Man (OMIM). Rather than treating each book as a whole that can be read sequentially, the Bookshelf represents the books as a collection of over 235 000 units of content, such as sections, subsections and chapters. Once within one of these content units, users can navigate to other areas of the book or search for specific content within the book.
