The Australia Telescope Large Area Survey (ATLAS) is the widest deep radio survey attempted so far, covering ≈7 deg2 across its two fields, the Chandra Deep Field South (CDFS) and the European Large Area ISO Survey South 1 Region (ELAIS-S1). ATLAS has extensive multiwavelength data, including optical, infrared and X-ray, to complement its ≈15µJy rms 1.4 GHz radio data. At these faint radio flux densities, star-forming galaxies begin to dominate the source population, and there is evidence for a composite population of sources with ongoing star formation that also contain an AGN. Understanding these faint radio source populations is essential for understanding galaxy evolution and what role is played by the AGN. I present preliminary results investigating the faint population of Compact Steep Spectrum sources in ATLAS, thought to be one of the earliest stages of the AGN life-cycle and possibly composite AGN/star-forming objects. Exploring this population will aid us in understanding the evolution of AGN as a whole and help to shed light on what triggers AGN.