Wine is a free and open-source compatibility layer to allow application software and computer games developed for Microsoft Windows to run on Unix-like operating systems. Developers can compile Windows applications against WineLib to help port them to Unix-like systems. Wine is predominantly written using black-box testing reverse engineering, to avoid copyright issues. No code emulation or virtualization occurs, except on Apple silicon Mac computers, where Rosetta 2 is used to translate x86 code to ARM code. Wine is primarily developed for Linux and macOS.

In a 2007 survey by desktoplinux.com of 38,500 Linux desktop users, 31.5% of respondents reported using Wine to run Windows applications. This plurality was larger than all x86 virtualization programs combined, and larger than the 27.9% who reported not running Windows applications.

Bob Amstadt, the initial project leader, and Eric Youngdale started the Wine project in 1993 as a way to run Windows applications on Linux. It was inspired by two Sun Microsystems products, Wabi for the Solaris operating system, and the Public Windows Interface, which was an attempt to get the Windows API fully reimplemented in the public domain as an ISO standard but rejected due to pressure from Microsoft in 1996. Wine originally targeted 16-bit applications for Windows 3.x, but as of 2010^[update] focuses on 32-bit and 64-bit versions which have become the standard on newer operating systems. The project originated in discussions on Usenet in comp.os.linux in June 1993. Alexandre Julliard has led the project since 1994.

The project has proven time-consuming and difficult for the developers, mostly because of incomplete and incorrect documentation of the Windows API. While Microsoft extensively documents most Win32 functions, some areas such as file formats and protocols have no public, complete specification available from Microsoft. Windows also includes undocumented low-level functions, undocumented behavior and obscure bugs that Wine must duplicate precisely in order to allow some applications to work properly. Consequently, the Wine team has reverse-engineered many function calls and file formats in such areas as thunking.^{[citation needed]}

The Wine project originally released Wine under the same MIT License as the X Window System, but owing to concern about proprietary versions of Wine not contributing their changes back to the core project, work as of March 2002 has used the LGPL for its licensing.

Wine officially entered beta with version 0.9 on 25 October 2005. Version 1.0 was released on 17 June 2008, after 15 years of development. Version 1.2 was released on 16 July 2010, version 1.4 on 7 March 2012, version 1.6 on 18 July 2013, version 1.8 on 19 December 2015 and version 9.0 on 16 January 2024. Development versions are released roughly every two weeks.

Wine-staging is an independently maintained set of aggressive patches not deemed ready by WineHQ developers for merging into the Wine repository, but still considered useful by the wine-compholio fork. It mainly covers experimental functions and bug fixes. Since January 2017, patches in wine-staging begins to be actively merged into the WineHQ upstream as wine-compholio transferred the project to Alistair Leslie-Hughes, a key WineHQ developer. As of 2019^[update], WineHQ also provides pre-built versions of wine-staging.

The main corporate sponsor of Wine is CodeWeavers, which employs Julliard and many other Wine developers to work on Wine and on CrossOver, CodeWeavers' supported version of Wine. CrossOver includes some application-specific tweaks not considered suitable for the upstream version, as well as some additional proprietary components.