This report was prepared in connection with the scientific evaluation of the ASTA programme in May, 2002. It consists of a comprehensive summary of the approaches and results from the different ASTA sub programmes. ASTA is presently in its fourth and last year of the first phase. The report is not intended to give a full description of all relevant aspects of the problem of transboundary air pollution but rather discuss some crucial problems and their possible scientific solutions. After the preparation and submission of this report, ASTA has been positively evaluated and will continue into its second phase. The evaluation reports as well as a letter of intent for the second phase of the ASTA programme are available on the ASTA web page (http://asta.ivl.se). Further information of the programme is also available at the web page. For those who wish to receive more information of the programme, there is a list of contact persons at the end of the report. Many of the ASTA phase 1 activities are currently in a state of intense evaluation and reporting and additional scientific results as well as synthesises and assessments will be prepared during the remainder of 2002.