A review of all of the known structural stereotypes of dimeric Pt(I) or Pd(I) systems with at least one bridging phosphido group is presented. The nature of the direct metal-metal interaction is affected by the number, nature, and disposition of the various coligands. It appears that in some cases a bent M-M bond is by itself a center of nucleophilicity. On the other hand, it is experimentally known that the bridging phosphido ligand is a competing nucleophile, giving rise to an agostic interaction in Pd-2, but not in Pt-2, derivatives. MO theory is used to outline the major electronic features and correlation between different prototypes. Besides a qualitative approach based on the EHMO method, DFT and MP2 methods were used to reproduce the experimental structures and to explore the possibility of unknown tautomers.