Mucins are a very abundant class of glycoproteins present on most internal interfaces in most organisms in the animal kingdom. They fulfill many functions related to hydration, lubrication, and protection and also in recognition events and cell signaling. Despite the great importance of mucins, it is fair to say that even today the understanding of the interfacial properties of mucins is limited. One reason for this is the great variation in mucin structure. Mucins can be secreted or they can be membrane‐bound, their molecular weight can be vastly different, and their charge density varies, but most importantly, the unlimited number of ways that the carbohydrate moieties can be assembled provides a structural variation that is enormous. Thus, different mucins behave differently in solution, they aggregate differently, and they have very different interfacial properties. This has yet not been investigated in a systematic manner and thus the structure–property relations are not fully clear. However, different mucins do show general structural similarities, and some general features of their interfacial properties also display similarities. This review seeks to elucidate these similarities and tries to relate them to common physical chemical characteristics, which are also key elements for their functions in living organisms.