The concept of collective reduction in working time (RWT) is gaining traction as an interesting labour policy in industrialized societies, praised for its numerous benefits across various domains. Although several countries worldwide have successfully initiated trials for shorter workweeks, Belgium appears to be adopting this policy at a slower pace, with only a few trials conducted over the past two decades. This is particularly noteworthy considering that an incentive system for implementing RWT was established 20 years ago. The COLORBEL project aims to explore two aspects of collective RWT in Belgium. Firstly, it plans to launch a pilot experiment in the country to evaluate the impact of a specific RWT policy – a four-day workweek with full pay retention – across four specific domains: wellbeing, productivity, employment, and environment. Both administrative and survey data will be gathered in three phases (before, during and after the experiment) in participating companies, which will ideally be used to conduct a Difference-in-Difference analysis. Secondly, COLORBEL aims to develop a comprehensive framework that identifies the drivers for and barriers to the adoption of RWT policies, to assess the effectiveness of existing measures established within the incentive system established in 2004. This will involve creating a typology of companies, conducting a literature review and carrying out semistructured interviews with companies that have and have not implemented RWT policies. To achieve these research objectives, COLORBEL will employ a blend of quantitative and qualitative analysis techniques, fostering collaboration between researchers from Ghent University and the Federal Planning Bureau. Beyond contributing to the academic discourse on RWT, COLORBEL aims to offer valuable policy recommendations to the cabinet of the Minister of Economy and Employment on the impact and potential of RWT.