The past decade has seen a population explosion in theories of modified gravity. These theories are intended as candidate explanations for the accelerated expansion rate of the universe, and are alternatives to the cosmological constant of the LambdaCDM model.

Testing each inhabitant of this 'theory zoo' individually is practically impossible. A more effective way to test gravity is via the construction of a parameterized framework that describes this host of theories in terms of a finite set of numbers. I will give an overview of the space of modified gravity theories and outline the construction of a new framework, the 'Parameterized Post-Friedmann formalism', that describes it. This approach is powerful because it tests for deviations from General Relativity in a very general way, independent of the particular theories that have been invented to date (or might be invented tomorrow).

The next generation of cosmological experiments should enable us to place constraints on such parameterized approaches, driving the modified gravity population into decline.