The zirconium-silicon and hafnium-silicon binary systems were investigated by means of Debye-Scherrer X-ray analysis, metallography, melting points, differential analysis techniques, and chemical analysis. Both silicide systems contain a D8(8)-type phase which is stabilized by trace impurities of oxygen and nitrogen. The binary phases present are: Zr4Si, Zr2Si, Zr3Si2, Zr5Si4, alpha- and Beta-ZrSi, and ZrSi2; in the hafnium system: Hf2Si, Hf3Si2, Hf5Si4, and HfSi2. The ZrSi phase undergoes an allotropic transformation at 1550C; the high temperature form is of the CrB type while the low temperature crystal structure is of the FeB type. Complete phase diagrams from 1100C up to melting are given.