This chapter describes how to use the Parse Service Routine in a Command Processor to determine the validity of command and subcommand operands. The first three sections, Overview of the Parse Service Routine (IKJPARS), Character types accepted by the Parse Service Routine, and Services provided by the Parse Service Routine, present the terminology and concepts that are necessary to understand the functions of the Parse Service Routine. The remainder of this chapter consists of a step-by-step explanation of how to use the Parse Service Routine, followed by detailed discussions of each of the steps in the process.