Resumen: Most companies operate on a linear economy that consists of ¿take, make, use and waste.¿ However, the growing impact of industries¿ emissions on the environment has aroused global concerns about their activities. As a result, companies are increasingly aware of the importance of implementing a circular economy (CE) with environmental, social and economic beneficial results. In this transition to a circular system, companies will need guidance, especially in the case of small and medium-sized enterprises (SMEs), which are the predominant type of company in the Organisation for Economic Co-operation and Development (OECD) area. Taking this into account, the objective of this chapter is to provide SMEs with a methodology to understand the value of CE for their corporate strategy, diagnose their business and design an action plan to facilitate the transition to the CE, allowing them to create value and gain a competitive advantage in the market. The CE could be addressed through six fields of action: take, make, distribute, use and recover goods and materials (Park et al. in J Clean Prod 18:1492¿1499, 2010; Stahel in Nature 24:6¿9, 2016), and a transversal field of action called industrial symbiosis. These six fields of action are the methodology¿s backbone. The CE methodology for an SME consists of the following steps: Diagnose the company¿s situation, through reflection on the current value proposal, the stakeholders and a preliminary diagnosis regarding its level of CE application through a proposed diagnosis tool. Analyze barriers and opportunities derived from the application of the CE. Propose a CE implementation plan. This chapter will explain, the process followed, and the various results obtained in the rubber-metal company. The proposed methodology makes an important contribution to SMEs¿ professionals regarding the step-by-step implementation of the CE using a real case that shows how to identify, plan and capitalize on the opportunities of the circular economy. The case study reveals how SMEs can start implementing the paradigm shift through environmental strategies that do not usually require high amounts of financial resources or technology. Moreover, the case study also highlights the relevance of the CE for creating value and a competitive strategy in the market.