This book presents a systematic and comprehensive overview of the authors' recent innovative research on the folding mechanics of deployable composite structures. It begins by introducing foundational concepts, including the energy method, variational principles, and the core theory of composite mechanics. The discussion then advances to detailed theoretical models addressing large deformations across various folding modes--such as the compression and bending of tape-springs, the behavior of helical structures, and the coiling of lenticular, tubular, and bistable composite booms. The book concludes by examining current challenges and offering insights into future research directions in this rapidly evolving field.