Final Report Summary - NIRG (New paradigms for InfraRed modifications of Gravity) Our project addresses theoretical and phenomenological properties of large distance modifications of the gravitational interaction. Such modifications are motivated bytwo main reasons: firstly, to find alternative explanations to the presence of dark matter or darkenergy in cosmology; secondly, to better understand the currently well accepted cosmological model,disentangling there what does from what does not depend on the large distance dynamics of gravityand extracting as much as possible new information on gravity from the latest cosmologicalobservations. For the second goal, it matters to have at hand alternatives to the standard cosmologicalmodel based on general relativity, to serve as benchmarks. During this project, several existing ideas have been tested against data and the internal theoretical consistency of other existing proposals has been checked. We have also proposed new ways to modify the gravitational interaction. In addition, the main outcome of this project may be the discovery of new theories and constructions linked to two different ways to modify the theory of general relativity, either by making gravity finite range (i.e. considering "massive gravity") or considering extensions of general relativity featuring extra fields interactions via derivatives.