Metal-to-semiconductor (M-S) junctions are of great importance since they are present in every semiconductor device. They can behave either as a Schottky barrier or as an ohmic contact dependent on the characteristics of the interface. We will primarily focus on Schottky barriers. This chapter contains an analysis of the electrostatics of the M-S junction, including the calculated of the charge, field and potential distribution within the device. This chapter also contains a derivation of the current voltage characteristics due to diffusion, thermionic emission and tunneling in Metal-Semiconductor junctions, followed by a discussion of M-S contacts and MESFETs.