Book excerpt: REXX is a general purpose language which is easy to learn. It contains an extensive library of powerful functions which greatly reduces the amount of coding necessary to write applications. The use of REXX in a wide range of environments simplifies the writing of applications to run under different hardware and operating systems, and its expansibility allows other components to make sure of REXX facilities and vice versa. Practical Usage of TSO REXX provides a concise source of information for the development and implication of applications using the REXX language. The author adopts a practical approach, using lists and diagrams to illustrate relevant points. This third edition, (previously titled Practical Usage of MVS REXX), has been revised to include the new REXX features introduced for the OS/390 TSO/E environment.