How do human resource practices strengthen open innovation (OI)activities? This inductive study of six cases leads to propositions exploring this question, which has not been empirically investigated yet. We investigate the relation between human resource practices and an employee's willingness to embrace OI in six cases that include the perspectives of chief executive officers (CEOs), human resource managers, and experts from Belgium, the Netherlands, and the United Kingdom regarding human resource practices in both small and large companies actively pursuing OI. The findings reveal that when implementing OI, it is people's thinking and attitudes