The book covers the essential areas prescribed in the diploma curriculum, beginning with Sources of Energy, a crucial topic in today’s era of energy transition, where conventional and non-conventional sources are discussed with emphasis on practical relevance. The subsequent chapters on Fuels and Combustion provide insights into the classification and utilization of fuels, along with the scientific principles of combustion, which form an integral part of power generation and thermal systems. Understanding the physical backbone of machines leads us to Machine Components, where standard elements such as fasteners, shafts, keys, and bearings are introduced. Special attention has been given to Gears and springs, as they are critical in the design and functionality of mechanisms used in industry. The chapters on Transmission of Motion explore the different modes of power and motion transfer using belts, ropes, pulleys, and chains, enabling students to visualize common mechanical systems with clarity. Following this, Mechanisms are explained to bridge the gap between theoretical concepts and their practical applications in machines. The final topic, Lubrication, emphasizes its importance in reducing wear and improving efficiency, making students aware of the science and practice of maintaining machine longevity. Each topic is explained in simple language and supported with diagrams and numerical examples to strengthen conceptual learning and practical applicability.