The current standard model of cosmology requires an as of yet unknown “Dark Energy” make up about ~70% of the energy content of the Universe in order to explain the observed cosmic acceleration. An alternative explanation for cosmic acceleration, though, is that our theory of gravity must be modified or extended. It is important to develop techniques to distinguish between these two explanations. We will discuss an approach which parameterizes deviations from the perturbed Einstein’s equations (often referred to as “modified gravity (MG) parameters”) as a way to test General Relativity and other theories of gravity. This approach has been implemented in the software package Integrated Software in Testing General Relativity or simply ISiTGR which is used to place constraints on the MG parameters. Some results from the latest cosmological data sets will be presented.