ESA's exciting and fast-track Mars Express mission is the first of the new flexible (F) missions, which are based on a new implementation scenario to maintain overall mission cost below a very stringent cost cap. The key features of an F-mission are streamlined management, up-front definition of the payload, and the transfer of more responsibility to industry. The cost ceiling is 175 M Euro for future F-missions, but only 150 M Euro for Mars Express. The scientific objectives of the mission include the remote and in-situ study of the surface, subsurface, atmosphere and environment of the planet Mars. ESA's Science Programme Committee preliminarily approved Mars Express in November 1998, provided sufficient funding would be available, and gave its full approval on 19 May 1999. The selection of the scientific payload for Mars Express was completed in early May 1998 whilst the spacecraft design was still undergoing competitive feasibility studies. Towards the end of 1998, Matra Marconi Space (MMS) was chosen as Prime Contractor for the entire spacecraft procurement programme. The payload is composed of seven instruments and a lander, Beagle 2, to search for traces of life on Mars. Beagle 2 is currently only confirmed until the end of this year and its continuation is subject to the agreement of a financial and technical plan by the end of 1999. ESA's aim is the implementation of a top-class mission at a much lower cost than hitherto achieved. Significant savings will be made by purchasing recurrent systems from ESA's Rosetta mission. A compressed implementation schedule, a new relationship between ESA, industry and the scientific community, and the exploitation of synergies between the ground operation systems of Rosetta and Mars Express will help the latter to stay within the allocated budget. The launch by a Soyuz/Fregat must take place within an eleven-day launch window opening on 1 June 2003.