After introducing the concepts of decoherence and entropy in simple quantum mechanical and field theoretical systems, I will discuss how to apply them in the cosmological setting of inflation. The model I will consider is a simple two field inflationary model, in which the inflaton couples to a spectator field. I will then show how the cubic interaction at the one loop level decoheres the inflaton field, and thus also the curvature perturbation. Finally, I will discuss under which conditions the effects of inflationary interactions can be observed in the cosmic microwave background radiation.