"Observations have shown that the expansion of the Universe is accelerating. At present, there is no physically motivated model to explain this, directly demonstrating that current theories of fundamental particles and gravity are either incorrect or incomplete. Understanding this phenomenon is consequently one of the most important outstanding problems in the whole of science. Perhaps the simplest solution is to postulate a new component of energy density with an effective negative pressure that forms 75\% of the present energy density of the Universe. There are many other theoretical ideas for explaining this phenomenon, which are often collectively referred to as ``dark energy''. The research in this proposal is designed to help to understand dark energy by setting constraints on the cosmological expansion. The spatial distribution of matter and its evolution are sensitive probes of the matter/energy content of the Universe. Consequently galaxy surveys, which trace this distribution, provide key avenues for understanding dark energy through a number of different techniques. One technique, which is the focus of the research proposed here, uses ``Baryon Acoustic Oscillations'' to constrain dark energy. Baryon Acoustic Oscillations are patterns of galaxies, initiated by sound waves in the early Universe, that form a fixed scale in the Universe whose true size we know. The apparent scale of these ``standard rulers'', when observed in galaxy surveys, constrains the distance--redshift relation and consequently how dark energy is driving the acceleration of the Universe. In this proposal, I request funding to set up a team to develop the novel techniques required to extract these distance measurements from the next generation of galaxy surveys, and apply them to measure dark energy properties. This will develop European leadership in a key future field of observational cosmology."