An excellent series of articles on UML state machines and on state machine theory in general …

• Part 1: The over simplification of the event-action paradigm
• Part 2: UML extensions to the traditional FSM formalism
• Part 3: Designing a UML State Machine

In particular, I like the practical examples and discussion of implementation options for various aspects of the notation.

This series of articles is taken from the book: Practical UML State Charts In C/C++, Second Edition by Miro Samek.