Teachers’ professional development is nowadays seen as key in efforts to improve education. Knowledge sharing is a learning activity with which teachers not only professionalize themselves, but contribute to the professional development of their colleagues as well. This paper presents two studies, aimed to explain knowledge sharing by teachers’ occupational self-efficacy and Human Resources Management (HRM). In the first study we examined the impact of HRM from a ‘content perspective’, and focused on a bundle of Human Resources Management practices, namely, high-commitment Human Resources Management (HC-HRM). Multilevel analyses of survey data from 410 teachers, from 30 teams, in one school, showed that high-commitment Human Resources Management strengthened the relationship between occupational self-efficacy and knowledge sharing. The second study examined the moderating impact of Human Resources Management from a ‘process perspective’. In this study we focused on ‘distinctive’ Human Resources Management: employees perceptions of a visible Human Resources Management within the school. Multilevel analyses of survey data from 282 teachers, from 47 teams, in four schools, showed that a distinctive Human Resources Management strengthened the relationship between occupational self-efficacy and knowledge sharing. Although the findings are encouraging and enabled us to formulate some practical implications, the study limitations also gave rise to suggestions for further research.