The coupling of calorimetric and microscopic techniques shows that the whole crystallization process for some Se100–x Tex (x = 10, 15) glassy alloys proceeds by two different mechanisms, which we call surface and bulk. These mechanisms are activated differently depending on the particular heating rate used and on the temperature of the isothermal heat treatment chosen. The nucleation frequencies and growth rates were determined from reflection polarized optical microscopy analysis, and a good agreement is found between these experimental results and predictions done by the classical nucleation and the normal growth theories. The apparent activation energy from the whole crystallization process which is obtained via differential scanning calorimetry is higher for Se85Te15 than for Se90Te10, and the relation with these values and those obtained from activation energies of nucleation and growth is established. A detailed discussion about the meaning of the different Avrami indexes found is presented.