Book excerpt: Broad interest and steady progress in the area of Group-IV (Si:Ge:C) semiconductor nanostructures, including quantum dots, wires and wells, has produced a new class of functional materials and devices with characteristic dimensions less than 50nm. This volume brings together scientists from different disciplines to discuss fabrication and characterization techniques and optical and transport properties, as well as applications of Group-IV semiconductor nanostructures. Fields such as photonic systems, nanocrystal memories, light-emitting and THz devices, nanowire-based interconnections and transistors are addressed. Topics include: nanoscale silicon-based photonic systems; Si/SiGe/SiN heterostructures and devices; Si/SiGe quantum cascade laser for terahertz; three-dimensional Si/SiGe nanostructures; Si nanocrystals and porous Si- light-emitting properties; Si nanocrystals and porous Si - other properties; Group-IV semiconductor nanowires; and rare-earth-doped Group-IV semiconductor nanostructures.