Following a description of highlights during the early period (1969-1974), a series of interesting developments and subsequent ramifications in the studies on semiconductor superlattices, quantum wells and heterostructures, are reviewed by dividing them into thee categories : GaAs-GaAlAs, InAs-GaSb and other systems, according to the host materials. The subjects include superlattice transport, optical absorption, lasers, photocurrent, luminescence, Raman scattering, magnetoquantum effect, modulation doping, quantized Hall effect, impurity states and excitons in quantum wells, far-infrared magneto-absorption, cyclotron resonance, polytype superlattices and InAs quantum wells