Microwave is a electromagnetic wave between infrared radiation and radio waves with a wavelength of 0.001 ~ 1 m and a corresponding frequency of 300 MHz ~ 300 GHz. When a material is in the microwave field, its polar or charged particles align themselves as soon as possible to the microwave electrical field direction, and heat is produced during this process due to friction. As compared with conventional electrical heating, microwave irradiation has the advantages of non-contact heating, faster response, quicker heating, less reaction time, more rapid product formation, lower reaction activation energy, etc. This book aims to present up-to-date knowledge of microwave irradiation, and is divided to 8 chapters. The Editors hope that the contents of this book supplies a good introduction of the up-to-date knowledge of microwave irradiation.