Rax is a mountain range in the Northern Limestone Alps on the border of the Austrian federal provinces of Lower Austria and Styria.

RAX or Rax may also refer to:

• Gallius Rax, character from the Star Wars: Aftermath trilogy of science fiction novels
• Hello Summer, Goodbye (Rax in the US), a science fiction novel by British author Michael G. Coney
• Radio Aurora Explorer, the first National Science Foundation sponsored CubeSat mission
• RAX, a 64-bit register in the x86 family of instruction set architectures
• IBM Remote Access Computing, called RAX, an obsolete System/360 time-sharing system
• Rax Roast Beef, a regional U.S. fast food restaurant chain
• RAX-2, a CubeSat satellite built as a collaboration between SRI International and students at the University of Michigan
• Retinal homeobox protein Rx, a protein that in humans is encoded by the RAX gene
• Ragnar Axelsson, a photographer