Diatoms are being used increasingly to assess short- and long-term environmental change, because they are informative, versatile, flexible, and powerful ecological indicators. Diatoms respond rapidly to changes in many ecological characteristics. Assemblages are usually diverse and therefore contain considerable ecological information. For this reason and because it is easy to obtain large numbers of individuals, robust statistical and multivariate procedures can be used to analyze assemblage data. Methods for collecting, analyzing, and presenting data have advanced rapidly in the past 5-10 years. Because of the power and versatility of diatoms, the future for their increased use as ecological indicators is bright. Improvements in techniques continue rapidly, and diatoms will no doubt be one of the main groups of aquatic organisms providing data to meet the growing need for information on environmental change in aquatic ecosystems.