Basement membranes are thin, extracellular matrices which separate the epithelia from their underlying connective tissue. Basement membrane has been viewed as a complex structure with its chemical composition varying, depending on the site of presentation. The principle constituents being collagenous proteins and non-collagenous substances like heparin sulphate proteoglycan, laminin, fibronectin, entactin or nidogen. By virtue of its anatomical location and highly complex composition, the basement membrane may have a key role in a wide range of epithelial-mesenchymal interactions. Basement membrane is considered to be a mirror that reflects the state of health or disease being altered in many disease processes. This book is a compilation of the structure, function and variations of basement membrane in health and disease.