A paper that changed my approach to designing state machines is "Statecharts: A Visual Formalism for Complex Systems" by Harel (http://www.wisdom.weizmann.ac.il

A paper that changed my approach to designing state machines is "Statecharts: A Visual Formalism for Complex Systems" by Harel (http://www.wisdom.weizmann.ac.il/~harel/papers/Statecharts.pdf http://www.wisdom.weizmann.ac.il/~harel/papers/Statecharts.p...). Statecharts (also called hierarchical state machines) are essentially generalized state machines which allow for nesting and parallel composition of states. The 'nesting' part is my favourite, since it allows one to delegate event handling logic shared by multiple states to a 'parent' state, reducing code duplication. The great thing about this paper is that you can glean most of its key ideas by just looking at the diagrams.