Since the beginning of the 1980's, research has continued to clarify and improve our understanding of the problern of the ecological impact of acidic precipitation. From September 15-20, 1985, Canada convened the the Muskoka Symposium on Acidic Precipitation to review progress and help chart the direction of future studies. The Conference was held in central Ontario, Canada, a region of heavy sulphate deposition where aquatic effects are evident. Approximately 700 people attended, over 500 of whom were research scientists. Over 400 papers were presented. Nearly 200 of the papers are included in these proceedings, which tagether give the present state of the art of acid rain research. The Conference focused on atmospheric science and aquatic and terrestrial effects. I have made some general observations on progress in clarifying issues and linkages between these areas of research. Out­ standing issues which require a great deal more work are identified. These are my views, influenced by personal bias and limited by my expertise. Atmospheric Seiences Three aspects were covered: measurement techniques, the actual measure­ ments, and source-receptor relationships.