The versatile and available GNSS signals can detect the Earth’s surface environments as a new, highly precise, continuous, all—weather and near—real—time remote sensing tool. This book presents the theory and methods of GNSS remote sensing as well as its applications in the atmosphere, oceans, land and hydrology. Ground—based atmospheric sensing, space—borne atmospheric sensing, reflectometry, ocean remote sensing, hydrology sensing as well as cryosphere sensing with the GNSS will be discussed per chapter in the book.