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 for broader sustainability impacts. Unlike established firms, start-ups can readily adopt ambitious circular business models (CBMs) without the risk of business model cannibalisation and with the agility to adapt to market trends. CBMs enhance value creation, delivery and capture resource flows in an optimised non-linear fashion. Scaling up CBMs is crucial for overall economic, social and environmental benefits. Hence, leveraging the key entrepreneurial ecosystems actors, such as universities, business incubators and related venture development intermediaries, is vital for start-up support. In this special issue, we have invited researchers to submit contributions that delve into the dynamics among start-ups, entrepreneurial ecosystems and the circular economy, aiming to enrich our understanding of the early stage start-up development process with the aim of promoting the circular economy at a firm, regional or national level. Circular start-ups are poised to play a crucial role in driving the transition to a circular economy and achieving sustainability goals. Their agility in adapting to changing market conditions and their propensity to adopt radical CBMs set them apart from incumbent firms. Consequently, they are expected to possess competitive advantages and excel in terms of development and growth. However, akin to conventional start-ups, circular start-ups may encounter substantial barriers to scale-up potentially exacerbated by their simultaneous pursuit of propositions that are desirable, feasible, viable, circular and sustainable. These barriers often stem from a lack of resources or capabilities during the developmental phase of their ecosystem. In the process of developing CBMs, start-ups must remain vigilant about their impact and stay mindful of potential negative rebounds. This awareness is crucial to navigating the complexities inherent in the circular economy landscape. Start-ups engaged in the circular economy typically embrace particular business models that demand distinct resources and expertise tailored to an economy's specific contextual needs. Furthermore, entrepreneurs in the economy require comprehensive support to grasp the intricate dynamics of related sectors, such as resource recovery supply chains and the valorisation of second-hand resources. They must also effectively engage with the ecosystem's network, often characterised by its weak and nascent connections. Currently, policymakers interested in providing new venture development support, particularly through targeted entrepreneurial growth, actively pursue incubation strategies. Therefore, depending upon the sponsor's objectives, incubation mechanisms (incubators, accelerators, science parks, etc.) are considered preferred policy tools for seeding new and innovative ventures. They have now become the lexicon of entrepreneurship ecosystem development in various parts of the world. Incubation mechanisms, integral to the entrepreneurial ecosystem, are crucial in seamlessly integrating these start-ups into specialised business networks and shaping the burgeoning circular economy's structure. Incorporating circular economy principles, such as waste minimisation, resource recycling and redefining product life cycles, into the business strategies of incubators could be highly beneficial. Additionally, re-evaluating and enhancing the list and profiles of partnersThis 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 for broader sustainability impacts. Unlike established firms, start-ups can readily adopt ambitious circular business models (CBMs) without the risk of business model cannibalisation and with the agility to adapt to market trends. CBMs enhance value creation, delivery and capture resource flows in an optimised non-linear fashion. Scaling up CBMs is crucial for overall economic, social and environmental benefits. Hence, leveraging the key entrepreneurial ecosystems actors, such as universities, business incubators and related venture development intermediaries, is vital for start-up support. In this special issue, we have invited researchers to submit contributions that delve into the dynamics among start-ups, entrepreneurial ecosystems and the circular economy, aiming to enrich our understanding of the early stage start-up development process with the aim of promoting the circular economy at a firm, regional or national level. Circular start-ups are poised to play a crucial role in driving the transition to a circular economy and achieving sustainability goals. Their agility in adapting to changing market conditions and their propensity to adopt radical CBMs set them apart from incumbent firms. Consequently, they are expected to possess competitive advantages and excel in terms of development and growth. However, akin to conventional start-ups, circular start-ups may encounter substantial barriers to scale-up potentially exacerbated by their simultaneous pursuit of propositions that are desirable, feasible, viable, circular and sustainable. These barriers often stem from a lack of resources or capabilities during the developmental phase of their ecosystem. In the process of developing CBMs, start-ups must remain vigilant about their impact and stay mindful of potential negative rebounds. This awareness is crucial to navigating the complexities inherent in the circular economy landscape. Start-ups engaged in the circular economy typically embrace particular business models that demand distinct resources and expertise tailored to an economy's specific contextual needs. Furthermore, entrepreneurs in the economy require comprehensive support to grasp the intricate dynamics of related sectors, such as resource recovery supply chains and the valorisation of second-hand resources. They must also effectively engage with the ecosystem's network, often characterised by its weak and nascent connections. Currently, policymakers interested in providing new venture development support, particularly through targeted entrepreneurial growth, actively pursue incubation strategies. Therefore, depending upon the sponsor's objectives, incubation mechanisms (incubators, accelerators, science parks, etc.) are considered preferred policy tools for seeding new and innovative ventures. They have now become the lexicon of entrepreneurship ecosystem development in various parts of the world. Incubation mechanisms, integral to the entrepreneurial ecosystem, are crucial in seamlessly integrating these start-ups into specialised business networks and shaping the burgeoning circular economy's structure. Incorporating circular economy principles, such as waste minimisation, resource recycling and redefining product life cycles, into the business strategies of incubators could be highly beneficial. Additionally, re-evaluating and enhancing the list and profiles of partners