Structures of rare-earth-platinum compounds are identified. RvPt 3 compounds (R = La, Ce, Pr, Nd, Sm, Gd) crystallize with the ThvFe 3 structure type. PrPt and NdPt have a high-temperature modification which corrresponds to the CrB type. R2Pt and RsPt 3 compounds crystallize with the Ni2Si and MnsSi 3 types, where R = Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Y for both structure types. Atomic parameters were refined from single-crystal intensities collected on Gd2Pt. The coordination polyhedra of Ni2Si are compared with those of the Fe2P type. It is shown that a greatly idealized version of the Ni2Si type can be derived by periodic unit-cell twinning of the cubic-close-packed element structure. A survey of the known R xPt compounds (x _>_ I) is given. These compounds are compared with those occurring in the corresponding Ni and Pd systems.