This document defines a CCSDS Asynchronous Message Service (AMS) for mission data system communications. The service and its protocols implement an architectural concept under which the modules of mission systems—distinct sequential flows of application control logic, whether called processes, tasks, or threads—may be designed as if they were to operate in isolation, each one producing and consuming mission information without explicit awareness of which other modules are currently operating. Communication relationships among such modules are self-configuring; this tends to minimize complexity in the development and operations of modular data systems. A system built on this model is a ‘society’ of generally autonomous interoperating modules that may fluctuate freely over time in response to changing mission objectives, module functional upgrades, and recovery from individual module failure. The purpose of AMS, then, is to reduce mission cost and risk by providing standard, reusable infrastructure for the exchange of information among data system modules in a manner that is simple to use, highly automated, flexible, robust, scalable, and efficient. This Recommended Standard specifies the protocol procedures and data units that accomplish automatic configuration of AMS communication relationships, dynamic reconfiguration of those relationships during operations, and the use of those relationships to accomplish the exchange of mission information among data system modules. The scope and field of application are furthermore detailed in subclause 1.2 of the enclosed CCSDS publication.