Between 1968 and 1983 some 13 spacecraft were built and launched by ESA on scientific missions to study a vast array of disciplines. In 1984, in order to guarantee coherence, balance and continuity to its space science policy, and following the example of NASA, ESA established its first long-term scientific programme which was given the name Horizon 2000 and covered the 1995-2007 timeframe. In 1992, at the request of the ESA Council, a survey committee was established with the purpose of identifying the main scientific objectives and technological challenges of future space missions and to design a new long-term scientific programme for the 2007-2016 timeframe. In 1995 the programme elaborated following the committee's recommendations was approved and was given the name Horizon 2000+. It was also decided to refer to the Horizon 2000 and the Horizon 2000+ plans as to the Horizons 2000 plan. In its present implementation plan, which is shown in Figure C.1, the Horizons 2000 plan comprehends 8 so called cornerstone missions (approximately one every four years) and a larger number of smaller missions, covering most key space science fields.
In addition to its all-European projects, and following the evolution towards ``Big Science'' which has made worldwide cooperation a fundamental requirement to carry out state-of the-art scientific research, ESA is currently participating in most major international space science projects and is planning to do the same in the future.
In particular, since excellence in scientific research can only be achieved by developing and having easy access to state-of-the-art instruments, the success of a scientific community strongly depends on the effectiveness of the policy of the correspondent space agency.