Collagen is the most abundantly found bio-molecule in mammals. The family boasts more than 30 different types of collagen. They are extensively found in extracellular matrix. Collagen molecules not only shape to the tissue but are also responsible for its organization and structural integrity. The collagen molecules interact with cells via receptors and guide cell proliferation, migration and differentiation. Owing to their extensive occurrence and functions; collagen disorders have far-reaching effects. This book focuses on the physiology and pathology of collagen. The brief overview of the Collagen types, structure, metabolism and functions is attempted. Working classification for collagen disorders and brief description of the collagen diseases are included in this book.