1. This paper provides the introduction to a special issue of Freshwater Biology devoted to papers dealing with aspects of the physical environment and ecology of alpine, glacial, high latitude and mountain streams. 2. Eleven of the sixteen papers were included in a symposium that formed part of the scientific programme of the North American Benthological Society Annual Meeting in Calgary, Alberta, Canada, in May 1993. 3. The contributions are a combination of reviews, overviews and primary research articles that deal with streams and ecological issues in Alaska, Nepal, New Zealand, Switzerland and southern Africa. Important issues considered include environmental consequences of river ice; altitudinal and temporal distributions of stream biota, especially macroinvertebrates; litter processing; and bryophyte production.