Computation models and specification methods seem to be worlds apart. The project on abstract state machines (in short ASMs, also known as evolving algebras) started as an attempt to bridge the gap by improving on Turing's thesis. We sought more versatile machines which would be able to step-for-step simulate arbitrary algorithms on their natural abstraction levels. The ASM thesis asserts that ASMs are such versatile machines. The guide provides the definitions of sequential, parallel and distributed ASMs.