After reviewing the various classes of objects, which make up the radio sky, I will present some recent results on the sub-mJy source populations based on the Chandra Deep Field South VLA survey, with some details on their evolution and luminosity functions. I will then present the solution to a problem, which has been unsolved since the discovery of quasars in 1963, that is the mechanism responsible for radio emission in radio-quiet active galactic nuclei. I will put things into perspective by providing also the "big picture". Finally, the relevance of our results to future, deeper radio surveys, including those with the Square Kilometre Array, will also be discussed. The talk is self-contained and requires no previous knowledge of radio astronomy or active galactic nuclei.