EUCLID is a satellite designed specifically to investigate dark energy and to reveal its nature using astronomical observations. It will observe hundreds of millions of galaxies distributed over a large fraction of the sky to track the dark energy, dark matter and gravity imprints left on the Universe's geometry and the formation of its structure. By measuring the apparent shapes of galaxies, distorted by the gravitational lensing effects and their distribution in the Universe, astronomers will be able to determine the nature of dark energy and whether the theory of general relativity is still valid on very large cosmological scales. The instruments are developed by a European consortium including more than 120 laboratories and 1200 researchers and engineers in Europe and United States. The consortium which is also in charge of the scientific exploitation of the mission is under the scientific responsibility of Yannick Mellier, researcher at the IAP. The IAP also leads the development of the image processing for the VIS instrument and contributes with numerical simulations of the Universe and to the scientific analysis of the final dataset, in particular the detection and interpretation of cosmological gravitational distortions.