In recent years, Rydberg atoms have been the subject of intense study, becoming the testing ground for several quantum mechanical problems. This book provides a comprehensive description of the physics of Rydberg atoms, highlighting their remarkable properties by reference to their behaviour in a wide range of physical situations. Following an overview of the basic properties of Rydberg atoms, their interactions with electric and magnetic fields are analysed in detail. The collisions of Rydberg atoms with neutral and charged species are described, and the use of multichannel quantum defect theory in the study of Rydberg atomic systems is discussed. Experimental and theoretical research in this extensive field is also reviewed, making the book valuable to both graduate students and established researchers in physics and physical chemistry.