Asynchronous transfer mode (ATM) is an electronic digital data transmission technology. ATM is implemented as a network protocol and was first developed in the mid 1980s. The goal was to design a single networking strategy that could transport real-time video conference and audio as well as image files, text and email. Two groups, the International Telecommunications Union and the ATM Forum were involved in the creation of the standards.

ATM is a packet-oriented transfer method that uses asynchronous time division multiplexing (TDM) techniques. It encodes data into small fixed-sized cells (cell relay) and provides data link layer services that run over OSI Layer 1 physical links. This differs from other technologies based on packet-switched networks (such as the Internet Protocol or Ethernet), in which variable sized packets (known as frames when referencing Layer 2) are used.

ATM exposes properties from both circuit switched and small packet switched networking, making it suitable for wide area data networking as well as real-time media transport. ATM uses a connection-oriented model and establishes a virtual circuit between two endpoints before the actual data exchange begins.

ATM is a core protocol used in the SONET/SDH backbone of the public switched telephone network.