I am working on inflation, large scale structure in modified gravity models, and cosmic superstrings. Within inflation, I am studying DBI inflation in particular, with conclusions that generalize to other k-inflation / k-essence theories. After studying both tunneling and eternal inflation for such theories, I am now fleshing out a mechanism that generates these kinds of theories as a low energy effective theory coming from general multi-field models where the fields have kinetic terms that are dependent on the values of other fields, such as occurs in supergravity models of closed string moduli. A long term goal is a better understanding of large perturbations in DBI / k-essence models. The modified gravity model I am studying is inspired by the Dvali-Gabadadze-Porrati brane-world model; in more mundane terms, it is a phenomenologically viable modification of gravity with a very light, but massive, graviton. My work is concerned with how large scale structure develops in this model. I am using N-body, particle-mesh codes to study this: first, on a short time scale, using a modified version of the Newtonian Poisson equation, followed by a more comprehensive solution of the full non-linear differential equations that describe the extra scalar degree of freedom that a massive graviton must exhibit. I will compare these results to galaxy survey data and other cosmological observations to place limits on these models. Finally, I am continuing to study the distinctive phenomenology of cosmic superstrings. Their contributions to the small angular scale power and B-mode polarization of the CMB could be seen within the next couple of years. In the meantime, I am working out their effect on the 21 cm radiation that will eventually be the richest resource for observational data.