This book gathers important information on the synthetic aspects of phosphonic acids, metal phosphonate hybrid materials, phosphonates as scale inhibitors, phosphonates as corrosion inhibitors, catalytic properties of metal phosphonates, magnetic and optical properties of metal phosphonates, phosphonates as drugs for calcium-related disorders, metal-bisphosphonates as controlled release systems, metal phosphonates for energy applications, gas capture and storage, imaging applications, electrocatalytic transformations, water splitting, sensing applications, for photodynamic applications, and several others.