This book describes the Solaris Modular Debugger (MDB), which is a general purpose debugging tool for the Solaris operating system. The primary feature of MDB is its extensibility. This book describes how to use MDB to debug complex software systems, with a particular emphasis on the facilities available for debugging the Solaris kernel and associated device drivers and modules. The book also includes a complete reference for and discussion of the MDB language syntax, debugger features, and MDB Module Programming API.