This chapter describes the boriding process and the parameters that govern it. It also describes the features of the obtained layers and the main applications of materials treated with this hardening process. The kinetics of growth of the Fe2B face is described using a mathematical model, in which the evolution of the growth of the boride layers is assumed to be controlled by the boron diffusion by means of a dimensional analysis of Fick’s second law. The evolution of the growth of the Fe2B face on a low-carbon steel surface is illustrated by contour diagrams that involve the main variables of the process (time and exposure temperature). This type of diagrams allows the optimization of the process as a function of the treatment parameters.