The DEC Alpha, also known as the Alpha AXP, is a 64-bit RISC microprocessor originally developed and fabricated by Digital Equipment Corp. (DEC), who used it in their own line of workstations and servers. Designed as a successor to the VAX line of computers, it supported the VMS operating system, as well as the DEC flavour of UNIX. Later open source operating systems also ran on the Alpha, notably certain BSD UNIX flavours. Microsoft supported the processor until Windows NT 4.0 SP6 and did not extend Alpha support to Windows 2000.

The Alpha 21064 was introduced in 1992 running at 200MHz (the Intel Pentium, in comparison, ran at 66MHz when it was launched the following spring). The 64-bit processor was a superpipelined and superscalar design. At the time, DEC touted it as the world's fastest processor. In July 1996 it was clocked at 500 MHz (the 21164PC), in March 1998 at 666 MHz and in May 2000 at 731MHz (the 21264PC). 1GHz and faster pieces were announced in 2001 (the 21364PC or EV-7), and are available since 2003 at 1.1GHz+. Around 500,000 Alpha based systems were sold to end-2000.

The production of Alpha chips was licensed to Samsung Electronics Company. Following the purchase of Digital by Compaq the majority of the Alpha products were placed with API NetWorks, Inc. (previously Alpha Processor Inc.), a private company funded by Samsung and Compaq. In October 2001 Microway became the exclusive sales and service provider of API NetWorks' Alpha-based product line.

Compaq announced that computers using Alpha would be phased out by 2004 in favour of Intel's Itanium. HP, new owner of Compaq, announced that support the Alpha series would continue for a few more years, including the release of the EV79 chip, but this will be the final iteration of the chip. The IA-64 is supposed to be the replacement of this series.

Ironically, in mid-2003, as the Alpha were about to be phased out, the fastest computer in the U.S, and second fastest in the world, was a cluster of 4096 Alpha processors.

A persistent report attributed to DEC insiders suggests the choice of the AXP tag for the processor was made by DEC's legal department, who were still smarting from the VAX trademark fiasco. After a lengthy search the tag AXP was found to be entirely unencumbered.