macOS Big Sur (version 11) is the seventeenth major release of macOS, Apple's operating system for Macintosh computers. It was announced at Apple's Worldwide Developers Conference (WWDC) on June 22, 2020, and was released to the public on November 12, 2020.

Big Sur is the successor to macOS Catalina (macOS 10.15). The release of Big Sur was the first time the major version number of the operating system had been incremented since the Mac OS X Public Beta in 2000. After sixteen distinct versions of macOS 10 ("Mac OS X"), macOS Big Sur was presented as version 11 in 2020, and four subsequent versions incremented the major version number, similarly to previous versions of Apple's other OSes.

For the first time since OS X Yosemite six years earlier, macOS Big Sur features a user interface redesign. It features new blurs to establish a visual hierarchy, along with making icons more square and UI elements more consistent. Other changes include a revamp of the Time Machine backup mechanism, and the addition of the Control Center (which was previously introduced, exclusively for touch devices, with iOS 7). It is also the first macOS version to support Macs with ARM-based processors. To mark the transition, the operating system's major version number was incremented, for the first time since 2001, from 10 to 11. The operating system is named after the coastal region of Big Sur in the Central Coast of California, continuing the naming trend of California locations that began with OS X Mavericks.

macOS Big Sur is the final version of macOS that supports Macs with Nvidia graphics cards, specifically the 15-inch dual graphics late 2013 and mid 2014 MacBook Pro models, as its successor, macOS Monterey, drops support for those models.

Providing some indication as to how the pre-release operating system may have been viewed internally at Apple during its development cycle, documentation accompanying the initial beta release of macOS Big Sur referred to its version as "10.16", and when upgrading from prior versions of macOS using the Software Update mechanism to early beta releases, the version referred to was "10.16". An exception to this was the Developer Transition Kit, which always reported the system version as "11.0". macOS Big Sur started reporting the system version as "11.0" on all Macs as of the third beta release.

To maintain backwards compatibility, macOS Big Sur identified itself as 10.16 to legacy software and in the browser user agent.

Unlike macOS Catalina, which supported every standard configuration Mac that Mojave supported, Big Sur drops support for various Macs released in 2012 and early 2013. Big Sur runs on the following Macs:

By using patcher tools (such as OpenCore Legacy), macOS 11 Big Sur can be installed on earlier computers that are officially unsupported, such as the 2012 iMac and the 2012 MacBook Pro. Using these methods, it is possible to install macOS Big Sur on computers as old as a 2008 MacBook Pro and iMac and 2009 Mac Mini running smooth with non-metal graphics.