Object-oriented inheritance has been in widespread use for a decade, and it is now realised that although inheritance is a powerful modelling tool with many associated advantages, its benefits are not automatically conferred on systems that simply use it. This book introduces a model of inheritance based around five fundamental inheritance relationships. Each relationship has a clear conceptual basis, representing a fundamental, specialised use of inheritance. The resulting model replaces a confused notion of inheritance with five distinct conceptual relationships supporting more precise modelling of systems and capturing the semantic intent of each use of inheritance within a system.