The gravitational acceleration of antimatter on the earth has never been directly measured. The theory of General Relativity (GR) predicts that gravity does not distinguish between matter and antimatter, and while there is excellent evidence supporting GR in matter-matter interactions, this prediction for antimatter remains to be tested. GR is also known to be fundamentally incompatible with quantum mechanics, and some work towards a quantum theory of gravity suggests that the matter-antimatter gravitational interaction may in fact differ from the matter-matter one. It has also been suggested that such a behavior of the gravitational force may provide a natural explanation for the dark energy inferred by cosmologists and for the apparent asymmetry of matter and antimatter in the universe. After reviewing some of the theoretical issues and previous experimental attempts, I will talk about the Antimatter Gravity Experiment, a new experiment that is being planning to measure the gravitational deflection of an antihydrogen beam with an atomic interferometer. In addition to possibly showing us that our understanding of gravity is incorrect, this experiment will be sensitive to a previously unobserved fifth forces that couples differently to matter and antimatter. Clearly the Antimatter Gravity Experiment has the potential to fundamentally change the way we view the universe.