This Special Issue is a collection of Review Articles written by the members of the Collaborative Research Centre (SFB) 348 of the German Research Foundation (DFG). Its aims are the development of new methods for nanometer-scale structuring of semiconductors, the experimental and theoretical investigations of such nanostructures, and the design and prototyping of novel devices for high frequency, optical and optoelectronic applications. This required coordinated research efforts by physicists and electrical engineers into both basic physical phenomena and device oriented questions.