This book covers the physical principles, modelling, fabrication and applications of Tunnel Field Effect Transistors (TFETs) and Fin Field Effect Transistors (FinFETs). This is intended to act as a reference for undergraduate, postgraduate and research scholars belonging to backgrounds of Applied Physics, Electrical and Electronics Engineering and Material Science. Of paramount importance is the need to understand the simulation aspects of these devices, the validity of mathematical models, basics on fabrication and details of applications of these nanoscale devices. The presentation of the book assumes that the reader has fundamental concepts of semiconductor device physics and electronic circuits. A course such as the one this book is intended to accompany and motivate both students and scholars to get involved in the research on TFETs and FinFETs. Further, this book can act as a reference for device engineers and scientists who need to get updated information on device and technological developments.