PUBSUB is a versatile, efficient, and scalable publish/subscribe system. This paper describes the architecture of PUBSUB together with some of its current capabilities. A version of PUBSUB optimized for event processing was benchmarked against the publish/subscribe systems BE-Tree and Siena, which also are optimized for event processing. PUBSUB processes events faster than Siena and BE-tree. On our tests, the speedup of the fastest version of PUBSUB relative to Siena was 98% on an average. The speedup range relative to BE-Tree was from 1.23 to 1.48 and averaged 1.36 on the uniform tests and PUBSUB was comparable to BE-tree on the Zipf tests. The faster times in PUBSUB were a result of very efficient data structures used in PUBSUB to store the subscriptions, and the fast matching algorithms developed to match events to subscriptions.