During the last decade the publish/subscribe communication paradigm gained a central role in the design and development of a large class of applications ranging from stock exchange systems to news tickers, from air traffic control to defense systems. This success is mainly due to the capacity of publish/subscribe to completely decouple communication participants, thus allowing the development of applications that are more tolerant to communications asynchrony. This chapter introduces the publish/subscribe communication paradigm, stressing those characteristics that have a stronger impact on the quality of service provided to participants. The chapter also introduce the reader to two widely recognized industrial standards for publish/subscribe systems: the Java Message Service (JMS) and the Data Distribution Service (DDS).