A question largely left unanswered in previous studies of firms’ use of HRM practices, and the consequences thereof, is why some firms adopt these practices while others do not. We examine empirically the determinants of firms’ demand for HRM pay, work and training practices with a special focus on the role of differences in the organizational structure of firms. For this purpose we merge data from a detailed questionnaire study of Danish private sector firms’ use of HRM practices with workforce information from linked employer-employee data. We find that firms with a Multi-divisional or a Hybrid structure have a greater demand for (incentive) pay practices and new work practices than companies with a Unitary (functional) form. Moreover, M- and H-firms train more of their employees than the U-firms do, suggesting that employer provided training is linked to the adoption of pay and work practices.