This book is for the programmer who needs to convert a program written in TSO-CLIST to TSO-REXX in the z/OS TSO/ISPF environment. You need some familiarity with both languages in order to do a conversion. This book will show the correspondences, or lack of them, between CLIST language features and REXX language features. CLIST language features are shown on the left-hand page, with the corresponding REXX language feature on the facing, right-hand page. TSO-CLIST dates back to the beginning of TSO in 1971. It truly is a legacy language. IBM continues to support it because so many of its customers have active, functioning CLIST programs in use. CLIST language is found only in one environment, the z/OS TSO/ISPF environment. Experience programming with CLIST is not readily transferable to any other environment. The REXX language is found mostly in the z/OS TSO/ISPF environment, and in QMF, CICS, DOS/VSE, and Netview. Knowing REXX makes you more valuable to your employer. The number of programmers who can understand CLIST language is diminishing. It is a good business decision to convert CLIST programs, where possible, to REXX programs. I'm sure most programmers will remember the nightmare of having to fix a program that is so old that no one left alive knows what the program is expected to do.