In the last few years there has been significant progress in the development of microfluidics and nanofluidics at the application as well as at the fundamental and simulation levels. This book provides a comprehensive summary of these changes describing fluid flow in micro and nano configurations. Whereas in their previous book entitled Microflows: Fundamentals and Simulation the authors covered scales from one hundred nanometers to microns (and beyond), in this new book they discuss length scales from angstroms to microns (and beyond). While still maintaining the emphasis on fundamental concepts with a mix of semi-analytical, experimental, and numerical results, this book outlines their relevance to modeling and analyzing functional devices. The text has been divided into three main subject categories: gas flows, liquid flows, and simulation techniques. The majority of the completely new developments in this book are in liquid flows and simulation techniques chapters with modified information throughout the rest of the book. This book can be used in a two-semester graduate course. Also, selected chapters can be used for a short course or an undergraduate-level course. The book is suitable for graduate students and researchers in fluid mechanics and physics and in electrical, mechanical, and chemical engineering.