Neutrinos are ubiquitous in cosmology and they always represent a substantial fraction of the energy density of the Universe. This makes cosmology a key arena to test neutrino properties. In this talk, I will first review the main cosmological implications of neutrinos. Discussing how the Cosmic Neutrino Background formed and the impact of neutrinos for BBN and the CMB. I will then discuss three topics that I find timely and interesting in the context of precision cosmology: 1) what is the value of Neff in the Standard Model, 2) what can cosmological observations tell us about neutrino self-interactions, and 3) how can one evade the very stringent cosmological neutrino mass bounds.
