This graduate text describes the multi-step model of photoemission as a sequence of quasi-independent stages sufficiently separated both in time and in space, and extends the multi-step model to internal photoemission by adding the interactions specifically related to the presence of the second condensed phase as a collector material. The experimental approaches to interface characterization are illustrated by experimental results obtained on interfaces of wide bandgap insulating layers. The closing chapters characterize the interfaces of high-permittivity insulating materials with silicon, high-mobility, and wide-gap semiconductors. Annotation ©2014 Ringgold, Inc., Portland, OR (protoview.com)