XAP might refer to:
- Apache XAP, (eXtensible Ajax Platform), a software product presently under development at the Apache Software Foundation
- XAP processor, a CPU architecture for computers, developed by Cambridge Consultants since 1994
- XAP (Extensible Authoring Publishing), an old name for Extensible Metadata Platform (XMP)
- XAP (file format), container format for mobile apps and Silverlight web apps
- XAP, The IATA airport code for Chapecó Airport
- xAP Home Automation protocol
- XAP, The ICAO Code for Midway Connection, operated by Fischer Brothers Aviation of the United States
XAP is the file format used to distribute and install application software and middleware onto Microsoft's Windows Phone 7/8/8.1/10 operating system, and is the file format for Silverlight applications. Beginning with Windows Phone 8.1, XAP will be replaced by APPX as the file format used to install apps on the Windows Phone platform, a move which was done by Microsoft in order to unify the app development platforms for Windows Store apps and Windows Phone apps.
XAP files are ZIP file formatted packages, however Microsoft has enabled XAP file encryption, meaning the file can no longer be opened with a standard ZIP extractor. The MIME type associated with XAP files is application/x-silverlight-app.
The Windows Phone Marketplace allows users to download XAP files to an SD Card and install them manually.
XAP is also the extension for XACT Audio Projects, openable with the Microsoft Cross-Platform Audio Creation Tool. Silverlight XAP Files are not openable with the Audio Creation Tool, and XACT XAP files are not archives.