Studies on zooplankton have been undertaken on the St. Lawrence Great Lakes for slightly more than one hundred years. Earliest workers were fascinated by the microscopic life found in municipal water supply intakes from the Great Lakes and in the invertebrate forms occurring in stomachs of commercially important fishes. These early inquiries prompted further investigations on the taxonomy and distribution of Great Lakes zooplantkon. By the late 1960s over 200 papers had been published on various aspects of zooplankton taxonomy and ecology in the Great Lakes. Focus in recent decades has been on the control of nutrient pollution and accelerated eutrophication in the Great Lakes. Since these efforts have been at least partially successful, work on ecosystem rehabilitation is being initiated. As part of these comprehensive Great Lakes management programs, lake-wide water quality surveillance studies have been established to assess the adequacy of nutrient control efforts. Although these surveillance programs have emphasized chemical monitoring, biological sampling has often been included. These studies have provided an opportunity to gain new understanding of zooplankton spatial and temporal distribution and community composition in the Great Lakes.