One of the greatest mysteries in the whole of science is that 75% of the Universe appears to be made of an enigmatic ‘Dark Energy’. A further 21% of the Universe is made from invisible ‘Cold Dark Matter’ that can only be detected through its gravitational effects, with the ordinary atomic matter making up only 4% of the total cosmic budget. These discoveries require a shift in our perception. I play leadership roles in several large surveys, in particular the $40M international Dark Energy Survey (DES), where I coordinate the entire science programme, with 200 scientists from 5 countries. DES will have its first light in October 2011, with observing from 2012 to 2017. I propose three Themes, which are interlinked: (1) Modelling the cross-talk of DES probes and a feasibility study for a spectroscopic follow-up (DESpec) which will allow testing modified General Relativity models as alternatives to Dark Energy; (2) Attempting for the first time to measure the as yet unknown neutrino mass from DES, including novel modelling of the non-linear power spectrum; and (3) Follow up of an intriguing excess in galaxy clustering on large scales we recently detected in our home-grown MegaZ-LRG sample, and developing new approaches to photometric redshifts. The research is interdisciplinary since it is connected to statistical methods as well as to High Energy Physics. The techniques developed will also be used for many other projects, including the ongoing Hubble Space Telescope CLASH survey of clusters and the planned ESA Euclid space mission. At this stage of my career, after founding the Cosmology area at University College London and playing a key role in setting up DES, I wish to focus on creative research to exploit DES with the help of four Post-docs. I believe this work will significantly influence the next paradigm shift in Cosmology, and it will make a major contribution to Cosmology in Europe.