Socket 939 is a CPU socket released by AMD in June 2004 to supersede the previous Socket 754 for Athlon 64 processors. Socket 939 was succeeded by Socket AM2 in May 2006. It is the second socket designed for AMD's AMD64 range of processors.

Socket 939 processors and motherboards became available in June 2004, and were superseded by Socket AM2 in May 2006. AMD has ceased the production of this socket to focus on current and future platforms.

Both single and dual-core processors were manufactured for this socket under the Athlon 64, Athlon 64 FX, Athlon 64 X2, Sempron and Opteron names. The Opteron 185 and Athlon 64 FX-60, both featuring a 2.6 GHz clock speed and 1 MB of Level 2 cache per core, were the fastest dual-core processors manufactured for this socket. The FX-57 ran slightly faster at 2.8GHz, making it the fastest single core processor supporting the socket 939 interface.

It supports dual channel DDR SDRAM memory, with 6.4 GB/s memory bandwidth. Socket 939 processors support 3DNow!, SSE2, and SSE3 (revision E or later) instruction sets. It has one HyperTransport link of 16 bit width that can run as fast as 2000 MT/s.

In regards to video expansion slots, Socket 939 systems can be found with both AGP slots and PCI-E x16 slots as well.

Processors using this socket have 64KB each Level 1 instruction and data caches, and either 256KB, 512KB or 1 MB Level 2 cache