The global shift toward sustainable development and energy efficiency has brought renewable energy resources to the forefront of scientific, environmental, and industrial discourse. As the world grapples with the challenges of climate change and depleting fossil fuels, understanding the fundamental principles of heat transfer becomes essential for harnessing, converting, and utilizing renewable energy efficiently. Renewable Energy Resources: Principle of Heat Transfer is an interdisciplinary textbook that bridges the gap between thermal sciences and renewable energy technologies. It introduces the core mechanisms of conduction, convection, and radiation, and applies these concepts to real-world systems such as solar collectors, geothermal systems, biomass combustion, and wind turbines.