The early universe is a “laboratory” for testing physics at very high energies, up to a trillion times greater than the energies reached by the Large Hadron Collider. The origin of structure in the universe is deeply tied to this extreme physics, which is imprinted in the primordial ripples seen in the cosmic microwave background (CMB). CMB data have thus far led the way in constraining early universe physics, and ESA’s Planck satellite is currently mapping the CMB at the highest precision ever achieved. However, next generation galaxy surveys – such as the Dark Energy Survey (DES), starting next year – will rival the CMB in their ability to unlock the secrets of the primordial universe. I will use the Planck and DES data to rigorously test the theory of inflation, the dominant paradigm for the origin of cosmic structure, and to seek signatures of new physics that are likely to exist at these unexplored energies.I have already played a leading role in bringing theory and robust data analysis together to understand the very early universe. This proposal aims, for the first time, to go beyond simply testing generic predictions of the inflationary paradigm, to gain a fundamental understanding of the physics responsible for the origin of cosmic structure. The keys to achieving this goal are: theoretical modelling at the cutting edge of fundamental physics (describing not just the inflationary period but also pre- and post-inflationary physics); advanced Bayesian and wavelet methods to extract reliable information from the data; a deep understanding of data limitations and control of systematics. The project will produce definitive results at the interface of cosmology and high energy physics, defining the frontiers of these fields well beyond the lifetimes of the surveys themselves.