On the 30th anniversary of the discovery of IgE, the last immunoglobulin identified, the discovery and subsequent naming of the immunoglobulins is recounted. The first immunoglobulin-like protein to be discovered was the Bence Jones protein or light chain in 1845. Over 100 years, later, the final isotype, IgE, was discovered. During this century, there have been various names for what we now know as IgA, IgD, IgE, IgG and IgM. There was also confusion over what constituted a "new' immunoglobulin and how it should be named. As a result the current nomenclature seems arbitrary; however, it reflects both a historical tradition of preserving the original name of the protein as well as a rational system designed in the early 1960s to codify the basic proteins of the humoral response.