In 1983 Milgrom proposed that the evidence for dark matter in spiral galaxies could alternatively be explained using a modified law of gravity, termed Modified Newtonian Dynamics (MOND). This prescription was inherently non-relativistic and so it remained unclear how it could be extended to situations where the dynamics of spacetime plays a crucial role. I will review the history of dark matter and modified gravity and discuss a relativistic model which contains MOND in a certain limit with a focus on how its predictions compare to those of dark matter on the largest, cosmological scales.