This book is a comprehensive guide to methodologies for analyzing reliability and optimizing maintenance in complex systems, spanning from initial design to operational stages. The book comprises 20 chapters, each addressing different research topics in the reliability and maintenance of complex systems. These chapters are authored by esteemed professors and researchers in the field of reliability engineering, and they are organized as follows: System Reliability Modeling (8 chapters), Optimal Maintenance Models (4 chapters), System Performance and Availability Analysis (3 chapters), and Reliability Testing and Accelerated Life Tests (2 chapters). The remaining chapters focus on reliability testing and life data analysis. The book offers an in-depth exploration of various techniques, algorithms, and practical industry applications, making it an invaluable resource for researchers engaged in system reliability analysis and maintenance optimization, as well as for practical engineers and industrial managers. This book will be useful to students, researchers, and engineers in understanding the latest research issues and techniques in reliability and maintenance engineering.