Industrial development of software systems needs to be guided by recognized engineering principles. Commercial-off-the-shelf (COTS) components enable the systematic and cost-effective reuse of prefabricated tested parts, a characteristic approach of mature engineering disciplines. This reuse necessitates a thorough test of these components to make sure that each works as specified in a real context. Beydeda and Gruhn invited leading researchers in the area of component testing to contribute to this monograph, which covers all related aspects from testing components in a context-independent manner through testing components in the context of a specific system to testing complete systems built from different components. The authors take the viewpoints of both component developers and component users, and their contributions encompass functional requirements such as correctness and functionality compliance as well as non-functional requirements like performance and robustness. Overall this monograph offers researchers, graduate students and advanced professionals a unique and comprehensive overview of the state of the art in testing COTS components and COTS-based systems.