As a particle cosmologist, I aim at constructing a consistent history of the early universe based on possible extensions of the two standard models of particle physics and cosmology. To this end, I build new physics models, explore their phenomenology and point out eventual signatures in the sky as well as in laboratory and collider experiments. Open questions that I am particularly intrigued by concern, i.a., inflation, preheating, reheating, the production of gravitational waves during cosmological phase transitions, baryogenesis via leptogenesis, the phenomenology of the neutrino sector at low energies as well as elusive particle candidates for dark matter.