This chapter provides an overview of silicide contacts to microelectronic devices and to present many important material advantages and limitations for a microelectronic applications. It discusses the short historical account of contacts to devices, followed by a description of the self-aligned process, and of the suitable characteristics of compatible silicides. A careful exercise with the calculation of the energy difference at each step of the phase formation sequence indicates that to the extent that the enthalpy or free energy values can be trusted, only the first phase richest in Ni, Ni₂ Si in the previous phase sequence and in the current one, would form by a diffusion controlled process. The primary purpose has concurrently changed from reducing contact resistance and improving contact reliability, to shunting the high resistivity poly-Si gate, and to improving the contact resistance in the source-drain.