ACT++ 2.0 is the most recent version of a class library for concurrent programming in C++. The underlying model of concurrent computation is the Actor model. Programs in ACT++ consist of a collection of active objects called actors. Actors execute concurrently and cooperate by sending request and reply messages. An agent, termed the behavior of an actor, is responsible for processing a single request message and for specifying a replacement behavior which processes the next available request message. One of the salient features of ACT++ is its ability to handle the Inheritance Anomaly---the interference between the inheritance mechanism of object-oriented languages and the specification of synchronization constraints in the methods of a class---using the notion of behavior sets. ACT++ has been implemented on the Sequent Symmetry multiprocessor using the PRESTO threads package.