This book aims at providing the reader with up-to-date knowledge about Tesla turbine features, mechanical design, and performance characteristics. A Tesla machine, in general, is characterised by the absence of rotating blades, therefore it is also called bladeless or boundary layer machine. In this book, suitable numerical approaches for the fluid-dynamic analysis are described, with practical examples related to physical prototypes designed, built and operated by the Authors. Interest in small scale turbines is growing mainly for energy efficiency and power recovery in a variety of applications. Considering small scales, conventional bladed turbines impose manufacturing limitations, lower performance and higher cost, which hinder their implementation. Tesla bladeless turbomachines are being re-discovered due to many advantages such as their simple design and ease of manufacturing with acceptable performance, especially for small-scale power generation and energy harvesting. To contribute to the spread of efficient and viable Tesla turbines (or expanders), this book presents holistic design guidelines to Tesla turbines, encompassing geometrical definition of Tesla rotor, of Tesla stator, of Tesla rotor-stator-casing assembly, providing practical correlations to take into account various loss mechanisms, and discussing the optimal design point definition for such type of century-aged but always young turbines.