The goal of the Luquillo Long-Term Ecological Research Program (Luquillo LTER) is to understand how changing climate and land use are affecting the environment of northeastern Puerto Rico. Luquillo LTER includes both terrestrial and aquatic studies, from the peaks of the Luquillo Mountains to the city of San Juan, encompassing strong gradients of both climate and land use. Luquillo LTER research applies to other islands in the Caribbean and similar tropical areas, and it is part of global networks of long-term environmental research in the United States and other countries (US LTER, International LTER) and tropical forest sites (Center for Tropical Forest Science - CTFS). Luquillo LTER has operated continuously since 1988, with support from the US National Science Foundation, The University of Puerto Rico, and the International Institute of Tropical Forestry - IITF (USDA Forest Service). See Luquillo LTER research proposals for descriptions of Luquillo LTER research projects and results, and see articles on Luquillo LTER mentioned below.