Integrated Conservation and Development Projects (ICDPs) emerged in the 1980s and 1990s, to reconcile the need to protect threatened natural areas and, at the same time, to foster human development. Increasingly, around the world, natural resources were being rapidly depleted. In some cases local communities were held responsible for over-exploiting these resources, even when for their subsistence. The present research was based on an intensive case study of an ICDP developed within the framework of the UNESCO World Heritage Convention and implemented around Midongy-Befotaka National Park, in the Southeastern Humid Forests of Madagascar. The main activities involved were linked not only to conservation (in particular, the management of the park), but also to human development, in areas such as education, health, and income-generating activities. This research attempted to identify the successes and failures of the case study ICDP, and its impacts on conservation and development, over both short and mid-length time periods (between 1 and 5 years). The research was informed by various conservation and development theories and Conventions, and their applications in the field, with special attention paid to the design, implementation, and evaluation of the ICDP case study. Methods used included PRA techniques, such as household surveys; the analysis of specific environmental and socioeconomic indicators; and an examination of results obtained for specific variables related to the United Nations Millennium Development Goals. The results demonstrated first that positive results for conservation can be achieved if development activities successfully encourage the participation of local people and bring them immediate and sustainable benefits; and second, that success is related to international, national, and local parameters that need constantly to be evaluated, rethought, and readapted to changes in the local and national contexts. The research ended during a particularly difficult time in Madagascar, a political crisis followed by an environmental crisis involving illegal logging in 2009. Thus the research also briefly focused on analyzing the main reasons for the environmental crisis, which appeared to be related mainly to past mistakes in Malagasy conservation programmes and ICDPs that had neglected to co-opt local people and national institutions. Finally, the research yielded several important lessons from the past and recommendations for the future.