The 24 projects of the National Science Foundation’s Long Term Ecological Research Network, whose sites range from the poles to the Tropics, from rain forests to tundras and deserts, and from offshore marine to estuarine and freshwater habitats, address fundamental and applied ecological issues that can be understood only through a long-term approach. Each project addresses different ecological questions; even the scale of research differs across sites. Projects in the network are linked by the requirement for some research at each site on five core areas, including primary production, decomposition, and trophic dynamics, and by cross-site comparisons, which are aided by the universally available databases. Many species and environmental variables are studied, and a wide range of synthetic results have been generated.