Heterostructure device concepts promise several advantages in micro- and optoelectronics. From the material point of view, the main obstacle to be overcome is the large lattice mismatch of silicon based heterostructures. One of the best of them, silicon germanium (SiGe) is lattice mismatched to silicon by up to 4% depending on its Ge content. Basic investigations on strained layer growth, interface properties, and deviation from equilibrium are done with SiGe / Si heterostructures. Early results are discussed in context with our recent understanding. The application focus of this review is devoted to micro- and optoelectronic devices which could be fabricated after solving or understanding the basic interface problems. This includes devices already in production, and those in emerging fields for inclusion in the next generation of integrated circuits, as well as a selection of future device concepts with high merits to be proven in experiment.