This book starts by introducing the different definitions/theorems for semantic equivalence and analysis them proving problems in them all. Then, it develops a sound definition and theory for semantic equivalence that is congrunt and develops a formal method to prove the equivalence. It then develops formal methods for automated derivation of testing sequences. These cover both control flow and data flow. These methods are proven to have the widest applicability and coverage in terms of discovering errors if there are. Then, we develop formal methods to transform formal specifications given by ISO Formal Description Techniques (FDTs). This has applications in building common semantic model for the various FDTs as well as in automated derivation of test sequences, and in automated derivation of conforming implementations. All these have been demonstrated by applying them to real standards. These are applicable to computer/communications protocols, distributed systems, and software systems.