Book excerpt: A review and discussion of new knowledge on the structure and function of mammalian alkaline phosphatases (APs) gained over the last 25 years. It covers: * The structure, regulation and expression of the AP genes * The three-dimensional structure of APs and mutagenesis work that further defined the structural/functional domains of the isozymes * The phenotypic abnormalities of the different AP knockout mice * Our current understanding of the in vivo role of the AP isozymes. The book also describes the possible use of APs as therapeutic agents and therapeutic targets and the many uses of these enzymes in clinical medicine and in biotechnology.