The European Commission, DG XII, has published the proceedings of the fourth European symposium on "Polar stratospheric ozone", held in Schliersee, Germany, in September 1997, as part of its series on air pollution research. The purpose of this symposium was to discuss the results of EU-funded winter research activities during 1996-1997, and to compare these results from previous winters. Several of these research activities, funded under the EU's Environment and Climate programme, involved the use of remote sensing and in situ instruments to investigate the formation and properties of polar stratospheric clouds over Northern Scandinavia in winter. Studies of the evolution of ozone and ozone loss were also performed using measurements from ozone sondes, aircraft, and balloons and from ground-based instruments, as well as from the GOME satellite instrument. The book contains the full texts of all the papers presented during the symposium, which covered eight fields: - Meteorology and dynamics; - Polar stratospheric clouds (PSCs), aerosols and microphysics; - Ozone measurements; - Modelling and observations of ozone loss; - Halogen measurements; - Other measurements; - Heterogeneous and homogeneous chemistry; - Instruments, algorithms, methods and validation. Contact details for all the participants in the symposium are included in a separate section at the end of the book.