Many concepts in Lean Construction are based on collaboration. In project delivery models such as Integrated Project Delivery (IPD), which relies on a high degree of integration, the success of the project depends particularly on the degree of collaboration between the project participants. But even in traditional project delivery models such as design-bid-build, construction management at risk or design-build the degree of collaboration can have a strong influence on project success. While many project parameters such as costs, deadlines, quality, changes or risks are measured and controlled within the framework of project management of construction projects, hardly any focus is placed on measuring and controlling the important factor of collaboration between the project participants in a project. Starting with the basics on collaboration, this paper describes the development of a tool called "Collaboration Barometer", which can be used to measure the degree of collaboration between the participants in a construction project and shows how the results are processed and what benefits are derived from them. The paper also includes experiences with the first applications of the tool and gives recommendations for its use.