Circular economy has gained traction within companies resulting in many exploring new product and business model combinations. Yet, to transition towards a circular economy on a societal level requires going beyond new product and market-based opportunities. To enable societal level change, ecosystem-level innovations are important and so collaboration plays a key role. Cities are considered in this paper as hubs of innovation playing a key role in transitioning to a circular economy. They are responsible for 80% of global resource consumption, with a high concentration of capital, data and talent spread over a relatively small geographic area; making them an important part of societal level transitions. The current work stresses the need to understand and support collaborations in transitioning towards a circular economy. This paper explores what factors influence collaborations and how organizations collaborate for a circular economy in the context of cities. An initial literature review resulted in a framework for exploration, which informed the set-up of the questionnaire. This helped in conducting semi-structured interviews with people ranging from founders, designers to engineers from six circular start-ups, which operate and utilize the resources in cities; to understand how different organisations collaborate in cities. Results showed they focus on operationalizing their innovation through engagement with various stakeholders. As they increased their visibility in cities showcasing their value, increasing the ways and number of engagements, the organisation engaged with people and organisations having similar values and grew by scaling through engagement. This paper elaborates the idea of scaling through engagement as a way for circular organisations to scale.