A guide by Les Cottrell.
All IBM Rexx manuals and redbooks.
Base on author training course at Computer Associates Training centre in Slough.
Detailed language introduction.
Summary of REXX Functions, Syntax, Symbols, Operators, and Instructions.
Old manual defining Rexx in the context of Systems Application Architecture.
This article gives six "rules of thumb" that should help get started in REXX if you already know C or Pascal (or, really, any of the children of Algol).