B lymphocytes express membrane-bound immunoglobulin molecules as antigen-specific, clonally distributed, cell surface receptors. Molecules with the same fine specificity can be secreted in large amounts into the body fluids by progeny of the clone, subsequent to antigenic challenge and appropriate stimulation into terminal differentiation. While this review is limited to the regulation of immunoglobulin transcription, it should be noted that immunoglobulin expression is regulated at the level of DNA, RNA and protein. A DNA recombination process determines the specificity of the antibody to be expressed, the immunoglobulin RNA level is regulated qualitatively and quantitatively, as is the mature immunoglobulin protein.