This book focuses on the principles and applications of maintenance and reliability engineering in industrial systems. It covers various types of maintenance, including corrective, preventive, predictive, and proactive approaches, emphasizing their strategic roles in reducing downtime and improving operational efficiency. The book explores failure mechanisms and modes, such as corrosion, fatigue, and wear, and provides tools for diagnosing and anticipating faults. Quantitative methods like ABC analysis, Noiret charts, decision trees, and criticality matrices are introduced to support data-driven maintenance decisions. Diagnostic methodologies using tools such as fault trees and Ishikawa diagrams are detailed, enhancing root cause analysis. The final chapters address predictive failure analysis using statistical models such as Weibull and Poisson laws, highlighting real-world applications in different industries. Designed for students, engineers, and professionals, the book offers a structured approach to managing maintenance effectively and improving the reliability and lifespan of industrial assets.