Euclid is an ESA mission to map the geometry of the dark Universe. The mission will investigate the distance-redshift relationship and the evolution of cosmic structures. It achieves this by measuring shapes and redshifts of galaxies and clusters of galaxies out to redshifts ~2, or equivalently to a look-back time of 10 billion years. It will therefore cover the entire period over which dark energy played a significant role in accelerating the expansion.

It will be about 4.5 meters tall and 3.1 meters in 'diameter' (with appendages stowed). The nominal mission lifetime is six years.
A large-amplitude (~ 1 × 106 km) halo orbit around the second Lagrange point of the Sun-Earth system (L2) has been selected because it offers optimum operating conditions for Euclid: a benign radiation environment, which is necessary for the sensitive detectors and very stable observing conditions, which are sufficiently far away from the disturbing Earth-Moon system. In addition, the amount of propellant necessary is very favourable compared to alternative orbits.

Thales Alenia was selected in June 2013 to build the spacecraft. EADS Astrium was selected to provide the science module including the telescope. The propulsion system will be built by OHB Sweden.