Planning theory is turning again towards the question of power, particularly in relation to recent claims to a new communicative planning 'paradigm'. This thesis investigates how Foucauldian discourse analytics, embracing concepts of discourse, power/knowledge, rationality and space can contribute in sensitising planning research to power. A Foucauldian approach is developed which problematises the construction of rationality in spatial planning processes, focusing on the institutionalisation of rationality in the tools that provide decision-support. The power relations that condition this construction process are investigated in a detailed case study of the treatment of environmental risks in the policy process for the trans-European transport network. Key events are analysed, as a new policy discourse of European space and mobility emerges and is institutionalised in an ED policy framework. A narrative of the micro-politics of power at work focuses on the construction of Strategic Environmental Assessment as the principal tool in institutionalising a new discourse of environmental integration into TEN-T policy discourse. The case study operationalises discourse analytics in a way which embraces social practices and institutional dynamics as well as texts, showing the value of a non-textually oriented research design. The result is a detailed analysis of how power relations affected environmental integration in a critical area of ED policy making. Discoursive struggles were found to shape the local struggles taking place within the policy process, between EU institutions, individuals within them, and other interests. The policy outcome for environmental risks was found to be heavily conditioned by these struggles. These findings contribute to general understanding of the struggles for hegemony between economic, political and environmental discourses in spatial planning at EU and other levels. The operationalisation of a Foucauldian discourse analytic approach in this study suggests its usefulness in planning research, as well as in exploring theoretical questions about the relations between discourse, rationality, power/knowledge and space in spatial planning.