This article explores the role of start-ups within entrepreneurial ecosystems in driving the transition towards a circular economy. It emphasizes the importance of understanding and supporting circular start-ups to achieve broader sustainability impacts. Unlike established firms, start-ups can adopt ambitious circular business models (CBMs) without the risk of business model cannibalization and with the agility to adapt to market trends. CBMs enhance value creation, delivery, and capture resource flows in an optimized, non-linear fashion. Scaling up CBMs is crucial for economic, social, and environmental benefits. Key entrepreneurial ecosystem actors, such as universities, business incubators, and venture development intermediaries, are vital for start-up support. The article highlights the challenges faced by circular start-ups, including financial, market, and knowledge barriers, and suggests that incubation mechanisms can play a crucial role in integrating these start-ups into specialized business networks. It also discusses the need for personalized training, regulatory support, and consumer awareness to overcome these challenges. The special issue includes six selected papers that analyze the interplay between start-ups, entrepreneurial ecosystems, and the circular economy from various perspectives and methodological approaches. These contributions provide valuable insights for policymakers and entrepreneurs, emphasizing the importance of sustainable practices in addressing climate change and resource challenges. Future research should deepen our understanding of how circular start-ups contribute to broader economic changes and facilitate the transition toward sustainability.This article explores the role of start-ups within entrepreneurial ecosystems in driving the transition towards a circular economy. It emphasizes the importance of understanding and supporting circular start-ups to achieve broader sustainability impacts. Unlike established firms, start-ups can adopt ambitious circular business models (CBMs) without the risk of business model cannibalization and with the agility to adapt to market trends. CBMs enhance value creation, delivery, and capture resource flows in an optimized, non-linear fashion. Scaling up CBMs is crucial for economic, social, and environmental benefits. Key entrepreneurial ecosystem actors, such as universities, business incubators, and venture development intermediaries, are vital for start-up support. The article highlights the challenges faced by circular start-ups, including financial, market, and knowledge barriers, and suggests that incubation mechanisms can play a crucial role in integrating these start-ups into specialized business networks. It also discusses the need for personalized training, regulatory support, and consumer awareness to overcome these challenges. The special issue includes six selected papers that analyze the interplay between start-ups, entrepreneurial ecosystems, and the circular economy from various perspectives and methodological approaches. These contributions provide valuable insights for policymakers and entrepreneurs, emphasizing the importance of sustainable practices in addressing climate change and resource challenges. Future research should deepen our understanding of how circular start-ups contribute to broader economic changes and facilitate the transition toward sustainability.