The chapter “Circular Economy and Green Transition: An Introduction to the Concepts” offers a comprehensive overview of two pivotal models in sustainable development. It begins by defining the circular economy (CE) and green transition (GT), emphasizing their significance in modern environmental policy and economic practices. Tracing the historical context, the chapter highlights the transition from traditional linear economic models to more sustainable approaches. Investigating into the theoretical foundations, the discussion illuminates the core principles of CE is to minimise waste and reinforcing natural systems—and compares them with linear economic practices. The principles of GT, including strategies for achieving sustainable development and appropriate policy frameworks, are also analysed. The chapter further breaks down the components and strategies of CE, covering design and innovation, resource management, and sustainable business models. For GT, it examines pathways and practices in energy transition, sustainable industrial practices, and policy governance. With the help of detailed case studies, the chapter presents successful implementations and best practices and providing insights into real-world applications and their impact. Addressing the challenges and barriers to CE and GT, the chapter detects economic, technical, logistical, social, and cultural obstacles. It also aspects ahead to upcoming directions, discussing emerging trends, policy evolution, and the crucial role of multi-stakeholder collaboration. The chapter emphasizes the importance of adopting CE and GT practices to accomplish a sustainable future, offering a hopeful outlook on the continuous journey towards environmental sustainability and economic resilience.