Virtual Storage Access Method (VSAM) is an access method that supports indexed files with one main key which must be unique and multiple alternate keys that may or may not be unique depending upon your requirements. VSAM also supports Relative Record Data Sets (RRDS) and Entry Sequence Data Sets (ESDS). Most of the parameters given here and all of the examples are for indexed files. Indexed files are refered to as Key Sequence Data Sets (KSDS). VSAM files must be defined before they can be accessed by a user program. The utility IDCAMS refered to as Access Methods Services is used to create, delete, and alter all components of the file structure. Samples of the parameters available can be seen in section Access Methods Services Reference Summary. Sample JCL to do items normally needed are shown in section Sample Job Streams. VSAM return codes are shown in section VSAM return codes.