The crystallization of thin-film, amorphous Co-Si alloys has been studied in the composition range of 42-80 at. % Si. Structural relaxation of the amorphous alloys preceded the crystallization. Crystallization temperature decreased slowly with increasing Si concentration, but showed a sharp decrease near the stoichiometric silicide compositions of CoSi and CoSi2. The crystallization of alloys close in composition to the disilicide (Co 0.33Si0.67 and Co0.29Si0.71) was a one-step process with an activation energy of about 1.3 eV and an Avrami exponent of 3. In situ kinetic studies revealed that for the stoichiometric Co0.33Si0.67 alloy, the Avrami exponent of 3 arose from three-dimensional crystal growth from nuclei whose density saturated at the early stages of the transformation. The heat release and the volume contraction during crystallization of the Co0.33Si0.67 alloy were measured to be 0.118 eV/atom and 0.6%, respectively. In the case of a Co 0.2Si0.8 alloy, which is considerably richer in Si than the disilicide composition, complete crystallization was achieved in a two-step process with a higher activation energy of 2.1 eV for the primary crystallization.