In order to effectively develop multi-agent systems (MAS) software, a set of models, technologies and tools are needed to support flexible and precise specification and implementation of agent-to-agent conversations, standardized conversation protocols, and corresponding agent behaviors. Experience trying to build complex protocols with the ZEUS and JADE agent toolkits motivated a substantial extension to the JADE agent behavior model. This extension (called SmartAgent) enables more flexible, reusable and precise modeling and implementation of agent behavior. We augment JADE behaviors with uniform message, timing and system events, a multi-level tree of dispatchers that match and route events, and a hierarchical state machine (HSM.) HSM is represented using UML statechart diagrams, and implements a significant subset of UML state machine semantics. Adherence to the UML standard helps bridge object-oriented to agent-oriented programming, and allows us to use industry familiar modeling language and tools such as Rose or Visio. These extensions were tested in a meeting scheduler prototype.