Many ecological phenomena occur on time scales of decades or centuries, and the need for long-term ecological research was recently emphasized in Likens' presidential address to the Ecological Society. In the past it has been difficult to investigate these phenomena with financial support from funding agencies. However, in 1980 the National Science Foundation established the Long-Term Ecological Research Program (LTER). LTER-sponsored studies are now underway in 11 sites representing different ecosystem types. The purpose of this article is to describe briefly the general characteristics of each site involved with stream ecology and to summarize the nature and objectives of stream research at these sites