A review on the crystal chemistry of oxocobaltates of alkaline earth and rare earth metals is presented according to the formula of the compounds, based on increasing metal and oxygen content. The well-known structures of perowskites and K2NiF4-type compounds and their higher homologues have been ignored and cross-referred to older publications. Cobalt shows mainly the oxidation states Co2+ and Co3+. In many cases it exhibits integer valences like Co2.28+, Co2.5+, Co2.54+, Co2.8+, Co3.5, and Co3.6+, referred in the ICSD database. The dominant coordination polyhedra are CoO4-tetrahedra and CoO6-oktahedra. In two cases a trigonal prismatic CoO6-coordination is observed. Composition, crystal structure, and oxidation state of cobalt often depend on the preparation conditions. In contrast to the alkaline oxides, the alkaline earth and rare earth oxides used for preparations are less reactive. Therefore the necessary reaction temperatures are much higher. In these cases single crystals for x-ray investigation were prepared by plasma-burner and CO2-LASER techniques.