The simplest inflationary models predict purely adiabatic primordial density perturbations. I present current constraints from the CMB and LSS on models with a non-adiabatic contribution, allowing all constrainable modes of isocurvature fluctuations. We find models with high non-adiabatic contributions (up to 60% of the CMB power) to fit current data. I discuss how future data will help constrain the initial conditions. I then describe the fast Markov Chain Monte Carlo techniques we developed to allow reliable parameter estimation, and discuss their application to diverse problems in cosmology and astronomy.