This chapter explores the uses of Schottky barriers to study properties of a-Si:H and also to make good contacts to devices. Schottky barriers allow the probing of band bending near the surface and the determination of the density-of-states distribution inside the energy gap. The height of a Schottky barrier can be obtained from the forward internal photoemission characteristics in the case of thermionic emission in nearly ideal diodes. The C(V) measurements yield the value of the built-in potential and the charge density in the depletion region, if it is uniform (and the deviation from uniformity if it is not). Additional information can be obtained by internal photoemission experiments. Time-of-flight measurements with Schottky barriers can give the potential profile in the depletion layer. The built-in potential can also be obtained from that forward bias at which the collection efficiency of photogenerated carriers tends to zero (the flat-band condition). Another area of study discussed by Nemanich is the structural change that occurs under the electrode due to atomic migration leading to compound formation (silicides) and to phase segregation. Structural changes affect the I(V) characteristics. In some cases, inter-diffusion appears to eliminate interfacial defects. Heavy doping of a-Si:H results in thin tunnelable barriers that can be used as ohmic contacts to devices.