Microsoft Windows XP 64-bit Edition is a version of Microsoft's Windows XP operating system designed to run on Intel Itanium family of microprocessors in their native IA-64 mode. It should not be confused with Windows XP Professional x64 Edition, which is designed for x86-64 processors. As of July 2005, Windows XP 64-bit Edition is no longer supported.

Two versions of Windows XP 64-bit Edition were released:

• Windows XP 64-bit Edition for Itanium systems, Version 2002 — Based on Windows XP codebase, which was released in 2001
• Windows XP 64-bit Edition, Version 2003 — Based on Windows Server 2003 codebase, which added support for the Itanium 2 processor, was released on March 28, 2003.

Windows XP 64-bit Edition wasn't marketed as the Itanium version one of Microsoft's other Windows XP editions ('Home', 'Professional', 'Media Center' or 'Tablet PC') but was a separate edition made solely for the Itanium processor and its 64-bit instructions. However it was mostly analogous to Windows XP Professional, but with some limitations:

• The original version lacks most media applications such as Windows Media Player, NetMeeting, Windows Movie Maker, and integrated CD burning, although WMP and NetMeeting were added in the 2003 version.
• Numerous old technologies such as DAO, Jet database were removed; most notably NTVDM and Windows on Windows are no longer present so support for MS-DOS and Win16 applications is absent.

However, unlike previous alternate architecture ports of Windows (Windows NT 4.0 for PowerPC, MIPS R4x00, and Alpha) Windows XP 64-bit Edition could run standard x86 32-bit applications through its WOW64 (Windows on Windows) emulation layer. While the original Itanium processor contains an on-chip IA-32 decoder, it was deemed far too slow for serious use (running at about 400 MHz), so Microsoft and Intel wrote a software 32 to 64 bit translator dubbed the IA-32 Execution Layer. It allows real time translation of x86 32-bit instructions into IA-64 instructions, allowing 32-bit applications to run (albeit significantly more slowly than native code).