This book reviews a series of functional and immunological studies of the human sperm proteome. Two of the most cited studies originate from the examination of capacitation-induced protein modifications, which led to the cloning and characterisation of two new phospho-regulated cancer-testis antigens, named AKAP3 and CABYR. AKAP3 is a member of the A kinase anchoring protein-family, which provides spatial and temporal specificity to the cAMP-PKA pathway. In addition to scaffolding PKA, PDE and protein phosphatases, AKAP members also bind proteins that share homology to the RII dimerization/docking (R2D2) domain of PKA’ regulatory subunit. CABYR likewise interacts with a diverse array of signal tranducer molecules via its SH3-, R2D2-, and proline-rich extension-like domains. AKAP3 and CABYR associate in high molecular weight multi-protein complexes, which appear to regulate the energy supply to and motion of the sperm flagellum. The putative functional role of the CABYR signalling scaffold in cancer cells is discussed.