The infinitely small and the infinitely large have always attracted the attention of human thought. In recent years, and particularly since the discovery of graphene, our knowledge of the properties of 2D matter has increased exponentially. Two-dimensional semiconductors acquire particular importance in this context: our habitual technology is silicon-based, presenting scale limitations. Being able to implement semiconductors at the nanoscale can strongly incentivize the nanotechnology revolution we are facing. The purpose of this presentation is to offer the viewer an overview of the optical properties of Transition Metal Dichalcogenides (TMDs), particular semiconductors with the thickness of a single atomic layer that gained enormous scientific interest in the last decade.