One of the most outstanding problems in physics and astrophysics today is the existence of dark energy, which is inferred from the apparent accelerated expansion of the universe. Dark energy is believed to comprise about 70% of the energy content of the universe today, however, it's nature is largely unknown. The simplest model is to assume that the dark energy is in the form of a cosmological constant. There are, however, good reasons to believe that the nature of the dark energy could be more complicated than this. Euclid is an M-class mission with a targeted launch in l2019. Its primary objective is to study dark energy, secondary objectives are covering most of cosmology and astrophysics. The main observational targets will be baryonic acoustic oscillations and weak gravitational lensing measurements. Euclid was selected as the second M-mission in ESA's Cosmic Vision programme on the 4th of October, 2011. This proposal is for the necessary funding of management and coordination of the Norwegian participation in Euclid (the direct costs of Norwegian contributions to instruments and science ground segment will be funded by the Norwegian Space Centre), for Norwegian participation in the Euclid Science Working Groups, and for completing a research project in the period 2012-2014 studying the evolution of linear and non-linear structures in the universe in a class of interesting cosmological models called chameleon models. This research project will already give significant constraints on such models when compared with existing data, but will especially give interesting forecasts for how Euclid data best can give constraints. Furthermore, the project will build competence in numerical simulations of growth of structure in non-standard cosmological models, something that will be essential in future Euclid research.