Currently one of the most exciting problems in cosmology is the nature of dark energy, which is responsible for the late time accelerated expansion of the universe. Dark energy modifies the distance-redshift relation, and governs the late time evolution of gravitational potentials in the universe. Therefore by observing large scale structure we can gain valuable information on the nature of dark energy. In this thesis we examine a particular theory of dark energy, known as elastic dark energy. Using weak lensing and the ISW effect, coupled with CMB and SNIa data, we find lower bounds for the sound speed of elastic dark energy. We also explore how this model behaves in the presence of collapsing matter.