Circular economy aims at maintaining the value of products, materials and resources in the economy, in circulation by closing material loops and minimizing waste generation. In recent years, interest in circular public procurement has increased as the role of public procurement has been recognized important but yet not fully exploited opportunity by public authorities such as cities and municipalities in their transition towards circular societies while providing companies with new business opportunities and growth. This study analyzed possibilities and opportunities of public procurement to promote circular economy. Different approaches and examples of circular public procurement were recognized by case studies. In addition, opportunities to promote circularity were recognized among preset sustainable or green procurement criteria. In accordance with the principles of circular economy, public procurement can promote closed loops by setting criteria and requirements on the extension of product lifespan, efficiency and/or intensity of use, efficient cycling of biological or technical materials, and securing of clean and non-risky cycles. This study formulated four approaches to circular procurement, including the procurement of better quality products in circular terms, the procurement of new circular products, the use of business concepts that support the circular economy, and investments in circular ecosystems. Several sectors and product groups were recognized as potential for circular procurement, such as construction, waste and wastewater management, transportation, food and catering, furniture and textiles. The study also suggests that several tools such as performance based procurement, use of life cycle assessment (LCA) and life cycle costing (LCC) as well as criteria concerning reuse and recycling of materials could promote circular procurement. Market dialogue and co-operation between different actors in the supply chains are important for the future development of circular procurement. In addition, education of procurers is essential for the adoption of new practices.