This book aims to elaborate the basics and recent advances of membrane distillation (MD) as the same shows promise for seawater desalination and wastewater treatment. Starting with fundamentals of MD processes, including the heat and mass transfer analysis, energy evaluation and mathematical modelling, text includes engineering and molecular design of MD membranes. Various types of hybrid systems, including freeze desalination (FD)-MD, MD-crystallization (MDC), pressure retarded osmosis (PRO)-MD and forward osmosis (FO)-MD, will be discussed in this book. Further, it summarizes the future of MD from both industrial and academic perspectives along with energy sources and economic analysis.