An ecological threshold is the point at which there is an abrupt change in an ecosystem quality, property or phenomenon, or where small changes in an environmental driver produce large responses in the ecosystem.  Analysis of thresholds is complicated by nonlinear response functions and by multiple factor controls that operate at diverse spatial and temporal scales.  These complexities have hindered the use of threshold concepts in environmental management despite great concern about preventing dramatic state changes in valued ecosystems, determination of critical pollutant loads and other threshold-based environmental problems.  In this talk, I will discuss the prospects for identifying and investigating thresholds, with a focus on management of specific ecosystems.