The book "Engineering Simulations as Scientific Instruments: A Pattern Language" offers a comprehensive introduction to CoSMoS (Complex Systems Modelling and Simulation), an innovative, pattern-based approach to developing trustworthy simulations. These simulations are of scientific value to researchers and credible to third parties. The focus is on three central aspects: the use of explicit models to capture the scientific domain, the development of an engineering simulation platform, and the analysis of results from the conducted simulations. Additionally, the importance of arguments is emphasized, which serve as evidence that the scientific instrument meets the requirements. Close collaboration between subject matter experts and simulation engineers is another key component of this approach. The book is divided into several parts that illuminate both the theoretical and practical aspects of the CoSMoS approach, supplemented by case studies.