Interface states at semiconductor junctions

The experimental and theoretical progress in understanding the electronic s tructure and the related parameters of Schottky interfaces and heterojuncti ons is reviewed. Particular emphasis is devoted to the solution of several historical controversial points, to the impact of novel ab initio theoretic al approaches, to new experimental techniques based on synchrotron light an d free electron lasers, to the efforts towards controlled modifications of interface parameters and to the foreseeable future developments of this vig orously progressing and:technologically crucial field.