A growing majority of the world's population lives in cities, and the concentration of people and critical services in cities increases their exposure to acute shocks and long-term stresses. Therefore, building resilient cities that are able to resist and absorb threats and are capable of adapting to and recovering from shocks and stresses is vital for the wellbeing of society. Although the literature offers several studies on how city resilience can be improved, operationalizing resilience is still a challenge. This article describes the different phases of the co-creation process followed in the development of a maturity model that can guide cities in assessing and future improving their resilience level. This co-creation process was conducted using different methodologies involving an interdisciplinary group of international experts who contributed their knowledge and experience to the development process of the maturity model. The outcome of this process is the final version of a maturity model that operationalizes the steps that should be taken to build city resilience.