The growth of bulk crystals of Ge_1-xSi_x alloys in the composition range 0 < x < 1 by the Czochralski method is reviewed. Fully single crystals 10 - 25 mm in diameter and 20 - 70 mm in length were successfully grown for low or high Si contents and partly single crystals were grown for intermediate Si contents. Si crystal is clarified to be useful as a seed for the growth of GeSi alloys in the whole range. The growth velocity for single crystal growth and the effective distribution coefficient are discussed in solidification of solid solution system. The variation of the composition in the grown crystal along the growth direction is explained satisfactorily assuming complete mixing of the melt and using the equilibrium distribution coefficient obtained from the phase diagram. The gravity effect in the melt originating from a large difference in the densities of Ge and Si should be taken into account to explain the composition of the grown alloys.