This first volume of the textbook Hydraulic and Thermal Machines introduces readers to all necessary fundamentals to understand and operate hydraulic and thermal machines. No prior knowledge in machinery is required. With an uncomplicated yet rigorous approach, it gradually guides bachelor students, with no prior knowledge in machines, from basic concepts such as dimensions and SI base and derived units, to more complex, mathematical and mechanical fundamentals of hydraulic machines, energy conversion processes, fluids, including real ones, as well as hydrostatics and hydrodynamics. In turn, the book gets into the basic structure and operating modes of pumps and turbines, ending up with the study of fluid dynamic transmission in hydraulic machines. Numerous examples are analyzed in detail, for a comprehensive understanding and effective learning, which will prepare readers to the second volume of this set.