This gold open access book gathers the proceedings of the ReSBE Conference, ReShaping the Built Environment through Sustainability and Circularity, held in Thessaloniki, Greece, on October 20–23, 2026. It explores transformative pathways toward a regenerative, resilient, and circular built environment, addressing current challenges and emerging approaches across buildings, infrastructures, cities, and regions. The contributions present new models, methodologies, technologies, case studies, and decision-support approaches aimed at accelerating the transition toward sustainability and circularity in the built environment. The proceedings cover a broad range of topics, including circular design and construction, sustainability assessment frameworks, lifecycle assessment and monitoring, digitalization and automation, climate adaptation and resilience, energy and carbon performance, innovative and bio-based materials, urban and regional circularity, governance and policy frameworks, financing mechanisms, stakeholder collaboration models, and societal and educational dimensions of sustainable transitions.