This thesis examines the transformation of two Southeast Asian national retail markets altered by the entry of globalising food and general merchandise transnational retail firms. The study examines the dynamic and often contested evolution of Malaysia and Thailand's retail systems from the 1990s to the mid-2010s and considers how domestic actors and transnational retail firms have shaped the nature and direction of market transformations. Central to this study is the examination of sector-specific regulatory frameworks devised in the early 2000s by Malaysia and Thailand's national governments to resolve market actor disagreements arising from increased competition and supply system changes initiated by transnational retailers. The research examines the role of state institutions in mediating and guiding the course of development in Malaysia and Thailand's respective national retail markets. This cross-national comparative study makes an original contribution to the growing economic-geographical literature on the globalisation of retailing by conceptualising national retail markets as dynamic, path-dependent and contested multi-actor sectoral systems that are continually shaped by the institutional and political landscape in which they are embedded. Key to this conceptualisation is the integration of theories explaining processes of globalisation and frameworks that identify patterns of national distinctiveness. Comparative capitalism research is integrated with relational economic geography perspectives in order to conceptualise the complex institutional settings in which national retail markets evolve and are embedded. In particular, the study mobilises the Variegated Capitalism approach to deepen understanding of the diverse causal processes driving national retail market transformation. Making use of qualitative research methods, representatives from both case country retail markets have been interviewed and various sources of documentation have been analysed in order to gain in-depth understanding of the contrasting trajectories of Malaysia and Thailand's national retail markets. Several key insights emerge from this thesis. Firstly, addressing a current lacuna within the retail globalisation literature surrounding the long-term effects of transnational retail firm entry into national retail markets, it unveils the strategies of resistance and competition by domestic market actors and the mediation of change by national governments through the application of sectoral regulation. Secondly, it highlights the intense negotiations that occur between market actors over the rules that guide economic action in sectoral systems. By examining the formation and implementation of formal regulation this thesis uncovers how different economic actors actively produce and reproduce national retail markets. Furthermore, through the analysis of regulation a wide variety of retail system transitions are revealed. Thirdly, it introduces a heuristic and conceptual framework through which the multi-dimensional nature of retail system change can be examined and linked to the diverse cross-connective globalising processes that contribute to creating distinct national economies. In so doing, this thesis adds to the knowledge about sources of spatial variegation in contemporary capitalism.