This volume presents a formal model of VHDL that clearly specifies both the static and dynamic semantics of VHDL. It provides a mathematical framework for representing VHDL constructs and shows how those constructs can be formally manipulated to reason about VHDL. The dynamic semantics is presented as a description of what the simulation of VHDL means. In particular it specifies what values the signals of a VHDL description will take if the description were to be executed. An advantage of the approach is that the semantic model can be used to validate different simulation algorithms. The text also presents an embedding of the dynamic semantics in a proof checker which is then used to prove equivalences of classes of VHDL descriptions.