The REXX programming language includes built-in functions that simplify programming. REXX Functions let you manipulate data strings or do mathematics simply with a minimum of programming effort. This book explains 78 REXX functions that you can use in your REXX programs. This book is about z/OS TSO REXX functions. A function is a built-in feature of the REXX language. Functions are always available to you when you are writing your program. They provide an easy way to manipulate data strings or to perform arithmetic on numbers. Using functions simplifies programming and provides reliability, because the functions were created and tested by the software manufacturer (IBM.) The Index is not like most indexes that list only language features alphabetically. They are no help if you don't know the name of the language feature. This index shows the common English language name for a feature, for example, "Convert decimal number" points you to the REXX equivalent D2C. You don't have to know that D2C means "Convert decimal number to character" in order to use the index. The examples are simple and clear and will show you the different ways to invoke, or use REXX functions in a REXX program. To aid you in finding the function that you need, one chapter is devoted to listing the functions, classified by what they do. Each of the built-in functions is shown in detail with examples of use. The functions are shown alphabetically. As a bonus, I've included several supplementary chapters to make life easier for the REXX programmer: 1. How to write REXX macros. 2. Compatibility Issues across platforms. 3. Precedence of Operators. What REXX processes first, in complex expressions? 4. How to execute TSO Commands, in Native Mode (Ready Mode) TSO, in ISPF Option 6, on the command line on ISPF panels, and in batch. 5. How to specify Dataset names in TSO commands, in REXX, and CLISTs. An explanation of TSO naming conventions. 6. The TSO commands that you are likely to use in your REXX programs, arranged by their function, with clear and simple examples.