Mike Cowlishaw and Linda Green have kindly provided the following partial bibliography of REXX books.

The REXX Language
M.F. Cowlishaw

English:  ISBN 0-13-780735-X  Prentice-Hall, 1985
          ISBN 0-13-780651-5  2nd edition, 1990
German:   ISBN 3-446-15195-8  Carl Hanser Verlag, 1988
          ISBN 0-13-780784-8  P-H International, 1988
Japanese: ISBN 4-7649-0136-6  Kindai-kagaku-sha, 1988

The NetRexx Language
M. F. Cowlishaw

ISBN 0-13-806332-X, 197pp, Prentice Hall, 1997

The REXX Reference Summary Handbook
Dick Goran

ISBN 0-9639854-3-4, 228pp, CFS Nevada Inc., 1994
http://www.toward.com/cfsrexx

Teach Yourself REXX in 21 Days
William and Esther Schindler

ISBN 0-672-30529-1, SAMS, 1994

Modern Programming Using REXX
Robert P. O'Hara and David R. Gomberg

English: ISBN 0-13-597311-2  Prentice-Hall, 1985
         ISBN 0-13-579329-5  2nd edition, 1988

REXX in the TSO Environment
Gabriel F. Gargiulo

ISBN 0-89435-354-3, QED Information Systems Inc.
320 pages, 1990

Using OS/2 REXX
Gabriel F. Gargiulo

ISBN 0-894-35449-3, QED Publishing Group

Practical Usage of REXX
Anthony S. Rudd

ISBN 0-13-682790-X, Ellis Horwood (Simon & Schuster), 1990

Using ARexx on the Amiga
Chris Zamara and Nick Sullivan

ISBN 1-55755-114-6, Abacus Books, 1991

The REXX Handbook
Edited by Gabe Goldberg and Phil Smith III

ISBN 0-07-023682-8, McGraw-Hill, 1991

Programming in REXX
Charles Daney

ISBN 0-07-015305-1, McGraw-Hill, 1992

Command Language Cookbook
Hallett German

ISBN 0-442-00801-5, Van Nostrand Reinhold, 1992

OS/2 2.1 REXX Handbook
Hallett German

ISBN 0-442-01734-0, Van Nostrand Reinhold, 1994

OS/2 REXX: From Bark to Byte
International Technical Support Organization (IBM)

IBM Document Number GG24-4199-00, 1993

REXX: Advanced Techniques for Programmers
Peter Kiesel

ISBN 0-07-034600-3, McGraw Hill, 1992

REXX Tools and Techniques
Barry Nirmal

ISBN 0-89435-417-5, QED Publishing Group, 1993

The ARexx Cookbook
Merrill Callaway

ISBN 0-96-327730-8, Whitestone, 1992

Writing OS/2 REXX Programs
Ronny Richardson

ISBN 0-07-052372, McGraw Hill, 1992

Writing VX-REXX Programs
Ronny Richardson

ISBN 0-07-9111911-5, McGraw Hill, 1994