Over a billion people worldwide live in informal settlements or “slums”, according to the United Nations, a growing figure which indicates the failure of urban planning and policy to address urban inequality. One of the primary reasons that urban planning has failed to engage effectively with urban informality is informal politics. In particular, clientelism—the provision of benefits to the poor in exchange for political support—is an important channel by which the urban poor access land and services in developing democracies, and is central to how many cities grow and function. Clientelism conflicts with the aims of planning and disincentivizes political leaders from implementing plans. Yet planning scholars have not systematically investigated how clientelism is related to informal urban growth nor provided guidance as to how planners might operate more effectively in clientelistic environments. This study aims to addresses this gap in planning research, by asking two questions: (1) Are clientelism and informal urban growth related, and if so, how? (2) Does clientelism in informal settlements impact urban planning, and if so, how do planners respond? This study uses mixed methods to answer these questions. Employing statistical analysis of a large global sample of cities to address the first question, it finds that cities in more clientelistic countries are more likely to see the growth of informal settlements that show signs of having been laid out spatially in advance of settlement. The study uses a qualitative case study of Ghana to address the second question, finding that while the major constraints on effective planning in Ghana are political in nature, planners have developed ways to try to resist the political pressures they face without open conflict with political leaders. The study offers recommendations for a ‘politically adaptive planning’ approach in Ghana which identifies and builds on what is already working for planners and the urban poor in their own political context, rather than emulating practices from elsewhere. The dissertation also outlines principles for the application of a politically adaptive approach to planning in other contexts.