Adopting circular bio-based building materials provides opportunities to mitigate greenhouse gas emissions and other environmental impacts of the construction industry. However, as these materials are mostly new and emerging, their contribution to achieving a sustainable built environment needs to be thoroughly investigated. To this end, this chapter first categorises these materials into three types, with specific examples for each category, to give an overview of the potential utilisation of these materials in the construction industry. Furthermore, it is reported that the adoption of circular bio-based building materials in both developed and developing economies is hindered by various barriers, which need to be investigated and addressed to promote these materials’ successful and widespread utilisation. To shed light on this aspect, the adoption barriers of these materials are investigated in the cases of Flanders in Belgium and Vietnam. A comparative study shows that while cost and risk-related barriers are the most critical barriers in Flanders, the government’s role-related barriers are deemed the biggest hindrance to these materials’ utilisation in Vietnam. Despite these differences, the government’s roles are essential to addressing barriers in both developed and developing economies. Finally, to unravel the sustainability performance of these materials, this chapter synthesises, analyses, and discusses findings from relevant studies identified in the existing literature. The results indicate that most existing studies are dedicated to assessing the environmental sustainability of specific materials, lacking those that evaluate the comprehensive sustainability of buildings. The sustainability assessment methods used in these studies, mostly life cycle assessments, have methodological issues that need to be addressed in future studies. Moreover, although circular bio-based building materials outperform their traditional counterparts in mitigating climate change and reducing production costs, their use does not always offer better economic and environmental sustainability.