EChO was proposed as an M-class candidate mission for the Cosmic Vision 2015-2025 programme in response to the Call for Proposals issued by ESA in October 2010. In February 2011 it was selected for further assessment and study.
An ESA-internal study was conducted in the Concurrent Design Facility (CDF) at the European Space Research and Technology Centre (ESTEC) with the goal of realizing a feasible, proof-of-concept mission. System-level studies of the mission concept were run in parallel with two Industrial partners; these were completed in July 2013.
Studies of the EChO instrument started in late 2011. These were undertaken by two independent consortia of scientific institutes - one led by University College, London (United Kingdom) and the other by the Max Planck Institut für Astronomie (Germany) - that were selected by ESA through an open call and financially supported by ESA Member States. A single consortium, led by University College, London was selected in February 2013 following a competitive open Announcement of Opportunity for the scientific payload and elements of the ground segment for EChO. The instrument study ran until September 2013.
On 21 January 2014, the five M3 candidate missions were presented to the scientific community, in Paris, France. The ESA Science Programme Committee selected PLATO as the third medium-class mission at their meeting on 19 February 2014.