This dissertation resituates C. A. Doxiadis in Post-War urban design history with a detailed examination of how urban growth and change was addressed by urban design strategies as applied in the master plan for Riyadh Saudi Arabia, undertaken between 1968 and 1972. The Riyadh master plan commission is important within Doxiadis' career, occurring in the midst of his prolific writing projects and approximately eight years after he completed the Islamabad master plan, his most renowned project. Most Post-War architects focused on the socio-spatial components of urban life, elaborating architectural projects that intertwined transportation, infrastructure, and concentrated on mass housing strategies. This dissertation argues that Doxiadis' contribution to urban design theory and practice during the Post-War period was to define a rational scientific methodology for urban design that would restructure settlements to enable urban expansion and change while addressing issues of community building, governance and processes of development. The applied urban design for Riyadh Saudi Arabia strongly exemplifies Doxiadis' rational strategy and methodology as outlined in Ekistics theory and the conceptual model of Dynapolis. The comparative analysis examines how Doxiadis applies the Dynapolis model in the urban spatial planning of Riyadh to organize urban territory at the macro and local urban scales, define neighborhood communities, and connect the new master plan to the existing spatial territory of the city. The longitudinal analysis contrasts the Doxiadis master plan, Riyadh's first urban development strategy, to the most recent comprehensive approach MEDSTAR to understand how the Doxaidis' urban design has sustained its spatial continuity over time. This dissertation makes two significant contributions. The first is to broaden knowledge of Post-War urban design specific to the spatial problem of urban expansion and change, and second to resituate Doxiadis within the Post-War history of urban design specifically revealing his previously unrecognized project of the Riyadh master plan undertaken from 1968-1972.