This is the first book dedicated to the glass transition since this concept became recognized as a distinct and independent field of investigation. The glass transition is a synonym for relaxation and dynamics in complex disordered systems, especially in liquids. It embraces time-scales ranging from picoseconds to years. The book describes and interrelates the following processes: cooperative alpha processes in a cold liquid, structural relaxation in the glass near Tg, the Johari-Goldstein beta process, the Williams-Götze process in a warm liquid, fast nonactivated cage rattling and boson peak, and ultraslow Fischer modes. By describing the salient facts, explaining and discussing the fundamentals, the author attempts to introduce a unifying concept for the entire material. The formulas, diagrams and references are carefully selected to illustrate the main current ideas about the glass transition.