Preparative methods, properties, and reactions of organofluorosilicates, M2 [RSiF5], have been reviewed. Since organopentafluorosilicates contain a doubly-negatively charged hexacoordinate silicon atom, their reactivities are quite different from those of neutral tetracoordinate organosilanes. The carbon-silicon bond in organopentafluorosilicates is readily cleaved by electrophiles or oxidizing agents such as halogens, NBS, CuX2, MCPBA, and TCNE, and various functional groups are selectively introduced to the carbon atom which has been attached to the silicon atom. The organic group in the silicate can also be transferred to other metals such as Cu (I), Ag (I), Pd (II), Hg (I), Hg (II), Tl (III), and Bi (III). The transmetalation provides various types of carbon-carbon bond forming reactions.