Einstein’s most famous legacy is his theory of gravity. As this theory did not allow for a static Universe, Einstein introduced an additional, arbitrary term in his field equations, the so-called cosmological constant. He called this the ‘biggest blunder of his life’, after Edwin Hubble discovered that the Universe is actually expanding. But Einstein might have been right after all. The cosmological constant has recently been re-introduced as so-called Dark Energy after observations indicated that not only is the Universe expanding, its expansion is even accelerating. However, there is another problem. The dynamics of galaxies demand the existence of yet another mysterious substance: Dark Matter. Dark Matter is the pillar of the formation of galaxies and the evolution of the Universe as a whole, yet it has never been detected. Alternative theories are now being developed that discard both Dark Energy, hence Einstein’s cosmological constant, as well as Dark Matter, hence his theory of General Relativity. Was Einstein right after all?