Hydroprocessing catalysts based on transition metal sulfides have been extensively used worldwide in refineries for upgrading heavy fractions to better quality fuels. The present work reviews the studies dealing with Anderson heteropolyanions (HPAs) and the derived dimeric structure for synthesizing hydrotreating catalysts. The development of new preparation methods based on HPA catalysts led to efficient catalytic systems due to better sulfidation allowed by a better dispersion of the oxidic precursor even at high metallic loadings. The increase of the Co/Mo ratio in the heteropolycompounds up to 0.5 was possible due to the formation of dimer cobalt salt. The association of Co and Mo at the molecular level in the same heteropolycompound preserved after the drying step during the catalyst preparation ensured the efficiency of the promoting effect with a higher quantity of the CoMoS active phase. This HPA-based system was further improved by the simultaneous use of HPAs and chelating agents.