Abstract. CMOS circuitry dominates the current semiconductor market due to the astonishing power of silicon electronic integration technology. In contrast to the dominance of silicon in electronics, photonics utilises a diversity of materials for emitting, guiding, modulating and detecting light. In the last ten years a big research effort was aimed to render Si an optical active material so that it can be turned from an electronic material to a photonic material. For some the future of Si-based photonic lays in "hybrid" solutions, for others the utilisation of more photonic functions by silicon itself. During the last two years many breakthroughs in the field have appeared. In this paper we will review what we believe the most important: optical gain in silicon nanostructures. 1. Introduction Silicon is the electronic material per excellence. Integration and economy of scale are the two keys ingredients for the silicon technological success. Silicon has a band-gap of 1.12eV that is ideal for room temperature operation and an oxide SiO