Since the 1960s the membrane-bound enzyme alkaline phosphatase (ALP) has been utilized in drug delivery. As it cleaves phosphate substructures from drugs, auxiliary agents, and even from the surface of nanocarriers, this enzyme enables the design of drug delivery systems that can alter their properties in the body on demand. Anionic nanocarriers exhibiting bioinert properties can alter their surface to interactive once having reached the target site as due to an ALP-triggered cleavage of anionic phosphate groups from their surface charge converts to cationic improving for instance cellular uptake. Moreover, features such as the accumulation of nanocarriers at the target site or a targeted drug release triggered by ALP can be introduced. In addition, ALP is utilized to improve the potential of numerous diagnostic systems. Within this review, one provides an overview about the activity, selectivity, and distribution of this enzyme, as well as the great variety of applications in drug delivery and diagnostics making use of it.