The urgent need to transform our patterns of urban development has been expressed not only by the scientific community but also in the policy arena. Current concerns relate to increasing urbanisation and global environmental trends in regard to resource scarcity, climate change and degrading environmental quality. Urban complexity, cross-scale impacts, socio-institutional diversity and adaptability become crucial when thinking about alternative development pathways. This dissertation seeks to explore why and how cities face change in this context by revisiting the concepts of resilience, sustainability and transformability. It is structured in two parts. Part I focuses on conceptual analysis and explores the theories of resilience and transformation applied to urban systems, looking at how they relate and couple with urban sustainable development goals. It makes use of theories related to the resilience of socio-ecological systems, transition management research and ecosystem service frameworks to illustrate the complexity of urban systems. Part II takes the city of Bilbao (Basque Country) as a case study to help understand resilience and transformation capabilities and explore their applicability in the field of energy. It focuses especially on the role of the cognitions of stakeholders and decision-makers in the uptake and management of sustainability transitions. Two participatory and semi-quantitative methodologies are used to understand stakeholders’ discourses and cognitive understanding of the urban energy system: the Q method and Fuzzy Cognitive Mapping. Conclusions drawn from the conceptual and empirical contributions to this dissertation highlight that resilience and transformability are key concepts in sustainable urban development. How decision and policy makers understand the complexities, i.e. the connections and interdependencies in urban system dynamics, is key in the process of defining transition pathways. Multidisciplinary, integrated, participatory approaches in the governance of sustainable urban transformation are crucial if unintended policy impacts are to be avoided and stakeholders are to be engaged in the quest for sustainability and resilience under climate change and resource scarcity.