This PhD dissertation represents an effort to understand individual behavior leading to decisions regarding natural resource use and compliance with conservation policy at the government and at the community levels through the analysis of specific cases in the Brazilian Amazon. I first analyze the case of smallholder land clearing along the Transamazon and BR-163 highways in the face of Brazilian Forest Code enforcement by the federal government. My hypothesis is that smallholder land clearing paths over time are affected by assessments of the probability of being caught violating the Forest Code. I develop a dynamic decision model that considers the potential benefits and costs accrued from land clearing through time by a representative smallholder and include her perception of the probability of Forest Code enforcement, unobserved to the researcher. I apply an endogenous switching regressions econometric model to data collected with a sample of 542 households in 2003 and 2013/14. I find that longer land tenure frontiers where there are opportunities for smallholders to transition to cattle grazing from agriculture deserve the attention of enforcement of land clearing laws and restrictions and that the use of the forest by a smallholder is a protective signal that must be considered and encouraged. My results suggest that alleged government efforts to enforce the Forest Code among smallholders in the sample region have been ineffective. The second case I analyze is that of fisher households that enforce community fishing agreements, known as accords, in the floodplains of the Amazon River surrounding the city of Santarém. My hypothesis is that individual households benefit from their own fishing accords enforcement effort through fishing time savings. A factor demand analysis applied to data collected with over 600 households reveals that statistically important drivers of labor demand and fuel include the level of dedication of a household and its history in implementing fishing accords, the landscape, the flood cycle, the distance to the main regional market and biomass. The average household fishing time savings from enforcing accords range between 59 and 36 eight-hour days for a six-month-period, an important argument for continuing the enterprise. / PHD

À la suite de l'effondrement de l'Union soviétique, les états nouvellement formés de l'Asie centrale ont entrepris, à différents niveaux, des réformes de leurs secteurs agraires. Du point de vue de l'utilisation de l'eau d'irrigation, les réformes consistent notamment en des changements aux régimes fonciers et dans la décentralisation de la gestion du système de drainage et d'irrigation. La plupart des institutions qui, durant l'époque soviétique, géraient le système d'irrigation et de drainage ont été abolies. Cela a créé un vide institutionnel et permis le développement d’institutions au niveau local qui puissent être participatives et appartenir aux utilisateurs. Pourtant, le contexte historique et contemporain de la région pose des défis particuliers pouvant nuire à un tel développement. Les associations d'utilisateurs d'eau ou le gouvernement local gèrent l'irrigation et les systèmes de drainage au niveau local. Ces associations représentent souvent des initiatives conduites par les donateurs internationaux. Parallèlement, les institutions informelles et les modes traditionnels de coopération qui ont survécu à l'ère soviétique deviennent importants et quelques institutions créées durant cette ère demeurent toujours pertinentes. Cette recherche consiste à évaluer le rôle d’action collective dans un système de gestion d’irrigation et de drainage dans le bassin versant de la rivière Syr-Darya dans un contexte changeant concernant les droits d’usage de l'eau et de la terre. L'étude cherche à (1) saisir l'importance de l'eau d’irrigation dans les moyens de subsistance des utilisateurs dans la région de recherche; (2) explorer certaines caractéristiques des institutions formelles et informelles à travers lesquelles les fermiers dirigent des systèmes de drainage et d’irrigation; et (3) identifier les institutions qui appuient l'action collective et celles qui entravant son développement. La méthodologie de recherche repose une revue bibliographique et sur un travail de terrain dans la vallée de Ferghana, au Kirghizistan, entre le 30 avril et le 31 juillet 2008. Les résultats de la recherche sont présentés comme une étude de cas. / Following the collapse of the Soviet Union, the newly independent countries of Central Asia undertook reforms of their agrarian sectors with varying degrees of speed and depth. In general, the reforms consisted of changes in the nature of land tenure and in the decentralization of irrigation and drainage management. Through these reforms, former state management institutions were abolished leaving an institutional vacuum that presented an opportunity for the development of local-level management institutions. However, the historical context of the region poses particular challenges that may impede users to capitalize on such opportunities.     Water User’s Associations or the local administration manage irrigation and drainage systems at the local level. Water User Associations represent international donor-driven initiatives to introduce equitable, democratic and participative institutions for irrigation and drainage management. There are indications that those informal institutions and traditional modes of cooperation that survived the Soviet era are gaining importance. This study maps out the various institutions, defined as "rules in use", that farmers employ to manage the irrigation and drainage system in the Ferghana Valley within the context of changing land and water rights. The key objectives of the study are (1) to understand the importance of irrigated water for local livelihoods in the research area; (2) to explore certain characteristics of the formal and informal institutions through which farmers manage irrigation and drainage systems; and (3) to depict ways in which “collective action” in irrigation water management can be strengthened. The methodology consists of a synthesis of existing literature and fieldwork in the Ferghana Valley in Kyrgyzstan, from April 30 until 31 July, 2008. The results of the research are presented as a case study.