This document discusses message-oriented middleware (MOM). It begins with an introduction to MOM, explaining why it was developed and what it is. Then it covers some common MOM specifications including JMS, AMQP, STOMP, and MQTT. The next section discusses core MOM technologies like transport methods, persistence, and transactions. Advanced features of MOM such as high availability, performance, administration, and plugins are then outlined. Finally, the document briefly introduces alternative messaging technologies like ZeroMQ and cloud messaging before listing references for further information.