CD48, a CD2-related surface molecule, emerges as a critical effector molecule in immune responses. CD48 has a striking array of biological functions, among them adhesion, pathogen recognition, cellular activation, and cytokine regulation. Still, it is surprising that this mysterious molecule has not yet met its proper use as a therapeutical target in exaggerated immune disorders like hematopoietic tumors, autoimmunity and allergic reactions. Recently, CD48 was investigated in our laboratory as an effector molecule in human eosinophil function and in asthma. In this review, we shall discuss the known aspects of CD48 biology and describe the recent advances regarding the role of CD48 in human disease. Moreover, we shall review inventions making use of CD48, and discuss recent patents and the potential of CD48 as a future target for the therapy of allergic and other diseases.