This document is one of two tutorials designed to teach basic Mach programming skills. This manual explains the use of the Mach kernel calls. The companion document to this one, A Programmer's Guide to the Mach User Environment explains the use of higher level methods for implementing multithreaded programs and interprocess communication. Before writing programs that use the system calls directly, the user should be aware that the methods outlined in the other document may be used to solve his problem more simply.