Nanowires used to form by accident in many labs. They were a sign that something went wrong during crstal growth probably related to unintended impurities. Such samples deviated from the goal of atomically smooth, planar growth and were tossed into the trash. Today, nanowires are the focus of much international attention since their smaller size, large surface sensitivity, interfacial stability, is leading to novel device geometries. This talk will discuss problems related to growth mechanisms, doping and conductivity, crystalline defects, and optical properties of a number of heteroepitaxial compound semiconducting systems.