The primary documentation for the BeOS APIs is called the Be Book. This and all BeOS end user and developer documentation is in the
/beos/documentation/ folder on every BeOS CD-ROM in HTML format.
You can purchase the Be Developer's Guide, an O'Reilly book which is the latest printed version of the Be Book, either directly from O'Reilly or through Amazon.com.
The most current version of the Be Book are available on our Web site in various formats, in the documentation section: