The world strives for sustainable development to minimize environmental impact and resource consumption, where circular economy (CE) is emerging as a promising approach to address environmental, economic and social challenges associated with the Architecture Engineering Construction (AEC) industry. This study focuses on the implementation of circular economy principles in the End-of-Life (EoL) phase of existing buildings, aiming to identify gaps between theory and practice, specifically for reuse and recycle processes in AEC. The focal point are business models, processes and the regulatory framework in Austria. The research methodology employs semi-structured interviews with different stakeholders involved in activities within the EoL value chain, including architects, contractors, material suppliers, waste management organizations, demolition companies and regulatory authorities. Based on a literature review which addresses seminal issues for the implementation of CE in the building life cycle, this study compares findings from 12 interviews and the results from literature research, identifying gaps between theory and practice, with recommendations for a path forward.