"Workplace health promotion (WHP) are often depicted as an opportunity for pursuing a better and broader well-being condition under the assumption that working environments affect the physical, mental, and social well-being of individuals who spend large proportion of waking hours at work. While most empirical studies provided medical evidence to the effectiveness of WHP programs, scholars question the instrumental purposes of these programs founded on the belief that “healthy workers are better workers”. Little is known, for instance, about the design of WHP programs and their acceptance by workers. Our study addresses this gap, analyzing the co-production of a WHP program in an Italian research institute promoted by the healthcare authority, the local government and the national center for prevention and security in the workplaces. To this aim, we adopt the notion of boundary object investigate how different stakeholders reclaim to take part and being involved in this process, re-shaping their goals and their boundaries and why a WHP program or parts of it may be rejected or re-negotiated by its recipients. Our analysis reveals how each stakeholder contributes to re-shape the WHP program which emerges as the modular product of the composition of each matter of concern. Most notably, the strong rooting in a clinical perspective and the original focus on only workers at risk is gradually flanked by initiatives to involve all employees. Moreover, workers draw a line as for the legitimacy of employers’ intervention in the personal sphere of health promotion, embracing interventions addressing diet and physical activity while rejecting measures targeting smoking and alcohol consumption."