PLATO (PLAnetary Transits and Oscillations of stars) 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 March 2007. The proposal was submitted by Claude Catala (Observatoire de Paris, France) on behalf of a large consortium comprising scientists from across Europe. In October of that year it was selected for further assessment and consideration by ESA. An ESA internal assessment (phase 0) for PLATO began in November 2007, with a CDF study, part of the phase 0 process, running from December 2007 to January 2008. This led to a design that was suitable for a feasibility assessment and production of an Invitation to Tender to Industry (ITT). In April 2008, the ITT was issued, and following a competitive assessment Astrium (France) and Thales Alenia Space (Italy) were selected to run parallel industrial assessment studies lasting approximately one year. At the same time a consortium of ESA Member State scientists, the PLATO Payload Consortium, was formed to carry out an independent study of the payload, under the leadership of Claude Catala. All three studies ran in parallel and were completed at the end of summer 2009. A PLATO Science Consortium, formed in 2008 under the leadership of Don Pollacco (Queen’s University Belfast, United Kingdom), worked on the scientific preparation of the mission during this period. The report of the assessment study, which included the PLATO science case together with a synthesis of the industrial and instrument consortium studies, was presented to the scientific community in December 2009. In addition, an independent technical review of the assessment study was conducted by ESA. The recommendations of the review board were presented to the scientific community also in December 2009. On 18 February 2010, ESA’s Science Programme Committee recommended that PLATO, along with Euclid and Solar Orbiter proceed to the definition phase. In February 2011, the SPC selected the PLATO Mission Consortium for the provision of the payload and science ground segment components. In October 2011, Euclid and Solar Orbiter were selected for implementation, with PLATO maintained as a possible competitor for a future flight opportunity. In January 2013, a re-organised PLATO Mission Consortium was proposed to ESA, led by Heike Rauer from DLR, Germany. In March 2013, PLATO became a candidate for the M3 launch opportunity. PLATO was chosen as the third medium-class mission in ESA's Cosmic Vision Programme at the SPC meeting of 19 February 2014.