The formation of galaxies clusters through gravitational collapse depend sensitively on the properties of dark energy and dark matter. Through the study of these objects we hope to reveal the nature of these mysterious energy components of the universe. An important observational tool to this aim is weak gravitational lensing in which the projected matter density of clusters can be reconstructed from the subtle distortion of galaxy shapes by a foreground cluster. With the future Euclid satellite we will observe on the order of 100,000 galaxy clusters across a range of redshifts and as such be in a position to place considerable constraints on the equation of state of dark energy.