The core idea of this book is that object– oriented technology is a generic technology whose various technical aspects can be presented in a unified and consistent framework. This applies to both practical and formal aspects of object-oriented technology. Course tested in a variety of object-oriented courses, numerous examples, figures and exercises are presented in each chapter. The approach in this book is based on typed technologies, and the core notions fit mainstream object-oriented languages such as Java and C#. The book promotes object-oriented constraints (assertions), their specification and verification. Object-oriented constraints apply to specification and verification of object-oriented programs, specification of the object-oriented platform, more advanced concurrent models, database integrity constraints and object-oriented transactions, their specification and verification.