It is envisioned that asynchronous transfer mode (ATM) will provide scalable and high-performance application-independent security services. The ATM Forum Security Working Group is currently developing its phase one security specification, which defines a number of security services for the ATM user plane and control plane. In addition, mechanisms for carrying security-related messages and required security infrastructure mechanisms are also being defined. These mechanisms will allow an organization to build an ATM network which not only meets its performance objectives, but also its information protection requirements as specified in its site security policy. This article provides an overview of ATM security as specified by the ATM Forum Security Working Group. First, the ATM user and control planes' security services and mechanisms are described. Then the security messaging mechanisms at connection establishment and during the connection lifetime phases are discussed.