Recent results in the field of oxomercurate(II) chemistry are reviewed. The methods of preparation and the crystal chemistry of oxomercurates are discussed. The structures of the alkali metal oxomercurates (M 2 HgO 4 ), alkaline earth oxomercurates (MHgO 4 , CdHgO 4 ), rare earth oxomercurates, ternary oxomercurates (BaAg 2 Hg 2 O 4 and Ba 3 Pt 4 HgO 1 1 ) and the compounds Ba 2 Hg 2 Pd 7 O 1 4 , HgCr 6 , Hg 2 Nb 2 O 7 and HgV 2 O 6 are presented and analysed. The change in crystal chemical behaviour from oxomercurates to mercury-oxometallates is discussed.