Large-scale structure formation is arguably one of the most important problems of modern cosmology. The standard treatment is based on a point-particle picture and the corresponding Vlasov equation. We take a field-theoretic approach to this problem and identify how field correlators in curved-space time are related to classical particle distributions in phase-space. We obtain the Vlasov equation in a well-defined limit together with field-theoretic corrections which can be studied in a controlled way. We also take a fresh look at the initial conditions for the cosmic microwave background and large-scale structure formation by presenting a two-field inflationary model in which the inflaton couples biquadratically to a light spectator field. The spectator induces a rapid production of entropy which significantly alters the initial conditions for the cosmological evolution at the end of inflation by providing large, stochastically independent momentum fluctuations of the gauge invariant curvature perturbation.