Time Machine is the backup mechanism of macOS, the desktop operating system developed by Apple. The software is designed to work with both local storage devices and network-attached storage (NAS), and is commonly used with external disk drives connected using either USB or Thunderbolt. It was introduced in Mac OS X 10.5 Leopard, which was released in October 2007 and incrementally refined in subsequent releases of macOS. Time Machine was revamped in macOS 11 Big Sur to support APFS, which enabled faster and more reliable backups.

Time Machine creates incremental backups of files that can be restored at a later date. It allows the user to restore the whole system or specific files. It also works within a number of applications such as Mail and iWork, making it possible to restore individual objects (e.g. emails, contacts, text documents, presentations) without leaving the application.

Time Machine saves hourly backups for the past 24 hours, daily backups for the past month, and weekly backups for everything older than a month until the volume runs out of space. At that point, Time Machine deletes the oldest weekly backup.

For backups to a network drive, Time Machine allows the user to back up Mac computers over the network, and supports backing up to certain network attached storage (NAS) devices or servers, depending on the version of Time Machine. Earlier versions worked with a wide variety of NAS servers, but later versions required the server to support a recent version of Apple's Apple Filing Protocol (AFP) or a recent version of the Server Message Block (SMB) protocol, and Time Machine no longer works with servers using earlier versions of SMB. Some of the legacy support can be re-enabled by using hand-tuned configuration options, accessed through the Terminal. Apple's AirPort Time Capsule router, which was introduced in 2008 and discontinued in 2018, acted as a network storage device specifically for Time Machine backups, allowing both wired and wireless backups to the Time Capsule's internal hard drive. Time Machine may also be used with other external or internal volumes.

macOS Tahoe, released in 2025, is the last version of macOS to support AFP, with macOS Golden Gate onward only supporting Time Machine backups over SMB version 2 or later. Time Machine backups using AirPort Time Capsule routers will no longer function.

Time Machine was overhauled in macOS 11 Big Sur to utilize APFS, Apple's modern file system introduced in 2016, and makes use of APFS's snapshot technology. According to Apple, this enables "faster, more compact, and more reliable backups" than were possible previously with HFS+-formatted drives. An independent evaluation of this claim found that macOS 11's Time Machine implementation in conjunction with APFS was 2.75-fold faster upon initial local backup and 4-fold faster upon subsequent backups relative to macOS 10.15's Time Machine implementation using HFS+. A more modest yet nevertheless significant advantage was noted as well for backups to network-attached disks.

Local (i.e. USB- or Thunderbolt-connected) and network-connected Time Machine backup destinations are formatted as APFS by default, though Time Machine can continue backing up to existing HFS+ backup volumes." There is no option to convert existing, HFS+-based backups to APFS; instead, users who want to benefit from the advantages of the new, APFS-based implementation of Time Machine need to start with a fresh volume.

At least in some circumstances, encryption appears to be required (instead of merely optional) in the new version of Time Machine.