During the last four decades Tanzania has witnessed several macro and sectoral policy changes with a trickle down effect, shaping both the management of CPR and livelihoods of resource users and other stakeholders. The study was carried out in the eastern part of Same district, focusing on the highland-lowland CPR interaction among the Maasai pastoralists and the Pare who are predominantly farmers. The main objective was to analyse institutional changes underlying the management of CPR and the factors driving the change with emphasis to resources such as forest, water for irrigation and grazing lands. The theoretical approach for the study is based on Hardin characterization of the tragedy of the commons which is the basic problem of CPR management and the way contemporary scholars such as Ostrom and other researchers have tried to approach the problem. Primary data collection involved the use of anthropological methods and socio- economic surveys employing household questionnaires, key informant interviews, oral histories and participants observation. Secondary sources such as government reports were also used. The results indicate that institutional changes have resulted into resource use conflicts and the challenge is that these conflicts have been increasing. The types of conflicts included micro-macro conflicts between conservation authorities and resource users, inter-micro micro conflicts between farmers and between farmers and herders and intra-micro micro conflicts between people in the same family or household. The factors that increased the likelihood of institutional changes included political, technological and distance to markets. The study recommends ecosystem based institutional framework that is capable of accommodating the changes, improving people’s welfare and sustainable management of the CPR in the study area. The opportunity that is presented by the current policy changes where power is devolved to local resource users and stakeholders can be utilized to achieve the desired goals of sustainable management of the CPR.