The preparation, characterisation, and some properties of hydrido-rhenium complexes containing tertiary phosphines are described. The complexes [ReX4(PR3)2][X = halogen, X4= OCl3 or O(OR′)Cl2; R = alkyl or aryl groups], with lithium aluminium hydride, give three classes of hydride complexes of the general formulae [ReH7(PR3)2], [{ReHx(PR3)2}2](x < 7) and [ReH5(PR3)3] according to the actual phosphine used and the experimental conditions. The interconversions of the three classes of hydride complexes, their reactions with some neutral ligands and with acids, and their hydrogen deuterium exchange reactions with alcohols, hydrogen, and benzene are described. I.r., u.v., and n.m.r. spectral data and dipole moment data are recorded. These hydridorhenium complexes differ in a number of ways from their formally similar analogues of the Group VIII metals.