IBM High Level Assembler and Toolkit: HLASM - HLASM for MVS, VM, VSE, and the optional HLASM Toolkit Feature provide a development environment for System/390 assembler applications.

The Assembler Connection - at SimoTime site. Provides examples of 370 assembler coding techniques, instruction set, utilities.

Assembly Language: CS-310 - Text for the class 'IBM Mainframe Assembly Language Programming: CS310', by Dr. Laurence Leff at Western Illinois University.

Cole Software's XDC - A product for the debugging of Assembler language programs which execute in the OS/390 (MVS) operating system environments on IBM (and compatible) mainframes.

Dave's unofficial HLASM web page - Tips and Frequently Asked questions about IBM's High Level Assembler (HLASM) and S/390 Assembler programming

Hello, World program - MVS JCL (Assembly 370)

IBM Mainframe Assembler Programming - A collection of general articles on assembly language programming in IBM mainframe assembler (System 370/390). Individual articles cover specific instructions with programming tips.

Mainframe Express Assembler Option - Includes IBM mainframe high level language compatible macro assembler, linker, and emulator for seamless execution of COBOL and mainframe assembler applications on Windows PC.

NIH Computer Center - Using Assembler Language - Inhouse doc for NIH, but also contains general assembler programming tips.

Systems/Asm - Dignus' HLASM compatible assembler product for the IBM mainframe. It's available as a native assembler for OS/390 and z/OS, or as a cross-assembler hosted on Windows, AIX, Solaris, FreeBSD, Linux and Linux/390.

Tachyon 390 Cross Assembler - Now you can develop and maintain 370/390 assembler programs from your workstation! With the Tachyon Operating System you can test 370/390 Programs On Your Workstation!