The Einstein Equivalence Principle (EP) is probably the most fundamental postulate of physics. It is in particular the founding principle of general relativity and more generally the basic postulate of all geometric theories of gravitation. This central position has resulted in experimental tests of its different aspects (universality of free fall, universality of clock rates, Lorentz invariance) by numerous experiments with ever increasing precision making it one the best established postulates of physics today. However, most attempts at unification of general relativity and the standard model of particle physics lead to a violation of the EP, that would manifest itself in experimental tests. It is thus essential to pursue such tests with increasing precision and over a broad range of different experiments, as this provides one of the most accessible experimental windows to physics beyond the standard model.

In this aim several space experiments are being proposed to drive the uncertainty of EP tests below the levels achievable in ground experiments. The most advanced of these is clearly the MICROSCOPE project, a joined CNES-DLR-ESA mission that is planned for launch in 2015-16 and is expected to improve present limits on a possible violation of the universality of free fall (a central EP test) by at least two orders of magnitude. All technological challenges concerning the satellite and payload have been overcome and the mission is now ready to enter the final construction and assembly phase, waiting only for the "go-ahead" of the involved agencies.

The aim of this colloquium is to bring together leading researchers and all interested scientists in this area of fundamental physics, in order to present recent theoretical and experimental developments concerning tests of the EP, and to discuss a way forward towards improvements of experimental tests in ground and in space, and thus new insights into physics beyond general relativity and the standard model.