On 19 June 2012, the European Space Agency (ESA) formally adopted the largest collaboration of astronomers in the World, including scientists at the Max Planck Institute for Extraterrestrial Physics to help build the Euclid satellite. Euclid will study the ``Dark Universe" with great precision, tracing the distribution and evolution of the enigmatic dark matter and dark energy throughout the Universe.

"This is it", says Yannick Mellier from the Institut d'Astrophysique de Paris (IAP), and the lead of the Euclid Consortium (EC) selected by ESA, "ESA and the Euclid Consortium have worked for over 5 years to get to this point and now we are formally adopted to help build this exciting new space mission."

ESA today also endorsed a Multilateral Agreement (MLA) between thirteen European space agencies, NASA, and the Euclid Consortium, for the construction of key elements of the Euclid satellite, specifically the onboard instruments, software for analysing the data and the satellites scientific leadership.

"We have put together a fantastic team", continues Mellier, "with nearly 1000 scientists involved in our collaboration from across Europe and other parts of the World. We have experts in all aspects of astronomy, physics, satellite and software design."

The Euclid Consortium will provide two instruments to ESA, a visible imaging instrument, VIS, and a near infrared imaging and spectrograph instrument, NISP. These state-of-the-art instruments, equipped with wide field cameras, will create a huge amount of exceptional quality data over a large fraction of the sky.

Scientists at the MPE are responsible for the overall optical design of the near-infrared instrument; the institute will procure all lenses and their mounts and perform the corresponding functionality tests. The Ludwig Maximilians-University (LMU) is co-leading the preparation of ground-based complementary data and their merging with the Euclid visual and infrared data.

Both institutes are represented in several science working groups, in the Euclid Consortium Board and the ESA Science Team.

Moreover, the Max Planck Institute for Astronomy (MPIA) in Heidelberg will develop and manufacture the broad band filters as well as setting up the scientific data centre; the Argelander Institute for Astronomy (AIfA) at the Rheinische Friedrich-Wilhelms-Universitat Bonn will contribute to the software development and the scientific data centre.

"Euclid will provide a wealth of data on the three dimensional matter distribution in the universe", explains Ralf Bender from MPE, the German representative in the Euclid Board. "Not only will this give us interesting insights into the evolution of galaxies and galaxy clusters, we will also be able to better understand the accelerating expansion of the universe. Hopefully, this will bring us a big step forward in solving the riddle that is Dark Energy."

Euclid will use a 1.2-m diameter telescope and the two instruments to map the three-dimensional distribution of some two billion galaxies and of the dark matter that surrounds them, over one third of the whole sky. Stretched across ten billion light years of the Universe, the results of the mission will plot the evolution of structure over three-quarters of its history.

Euclid is now an official ESA mission and solidifies the Euclid Consortium at forefront of worldwide research into the "Dark Universe". German contributions to the Euclid mission are supported substantially by the DLR space administration with funds provided by the Federal Ministry of Economics and Technology.