Answering fundamental questions ranging from how the Solar System works, what the conditions for planet formation and for emergence of life are, to how the Universe formed, what it is made of and what its fundamental physical laws are, that is what Cosmic Vision 2015 - 2035, the long-term science Program of the European Space Agency, is aiming at. The Program is built around large-size missions - the pillars that achieve excellence and leadership in their science domain. These missions are the long- term anchors of the Program and are launched about every six years. The Program's mid-term flexibility elements are the medium-class missions, allowing it to respond to the evolving challenges of scientific research; they are launched about every two to three years, with typically two launches in between large-size mission launches. The pillars of the Program target the following science themes: exploration of the Jovian system, exploration of the highly energetic Universe and exploration of the gravitational Universe. For the first theme JUICE, the Jupiter icy moons explorer, is now in implementation with a target launch date in 2022. For the second one, ATHENA was selected, an advanced telescope for high energy astrophysics for a launch in 2028. For the third theme, mission concepts and technology developments for a gravitational wave observatory are being explored and assessed in preparation for a Call for Mission Proposals in the near future, with a target launch date in 2034. The first two medium-size missions for the program, being Solar Orbiter, a mission aimed at observing in detail the Sun and its environment, and Euclid, a dark energy mission, for launch in 2018 and 2020, are approved and well into implementation. The third mission, with a target launch in 2024 PLATO, a mission to explore transients of exo-planets and oscillations of the host stars, has been selected, and is under detailed definition. Following a call for the next medium-size missions, for a launch opportunity in 2026, three candidates are currently under assessment: ARIEL, aiming at characterizing the atmospheres of a large sample of exo-planets around near- by stars; THOR, targeting space plasma physics, in particular the interaction of the solar wind with Earth's magnetic field, and XIPE, an X-ray imaging polarimeter to make, for the first time, high-resolution measurements of the polarisation of highly energetic sources such as black holes, neutron stars or extragalactic jets. As a novel component in the Cosmic Vision Program, the first small missions, CHEOPS, a mission to characterize large exo-planets, and SMILE, a mission in co-operation with the Chinese Academy of Science aiming at investigating the interaction between Earth's magnetosphere and the solar wind, have been selected. This paper presents the science goals and the current payload optimizations for the future science missions of the European Space Agency.
