Purpose: The purpose of this paper is to report on a study that investigates the relationship between organisational factors, Teachers' Professional Development (TPD) and occupational expertise. Design/methodology/approach: A survey was administered among 152 Dutch teachers in secondary education. Findings: Analysis of the data revealed that of the organisational factors, in particular, the availability of organisational facilities contributes positively to the amount of TPD (that is, in training programmes, and social networks). Furthermore, participation in social networks appeared to have a positive influence on the development of occupational expertise. Research limitations/implications: The study is cross-sectional (all data have been collected at one point in time), and data have been gathered in one country, i.e. The Netherlands. It would be interesting to examine the proposed model in a longitudinal study, in order to address issues of causality. More research is also needed to explore the extent to which the findings would generalise to other occupational settings and/or to other countries. Owing to the relatively small sample size, a mediation model was not empirically tested. Future research using larger sample sizes is needed in order to test whether participation in learning activities (partially) mediates the relationship between organisational factors and occupational expertise. Practical implications: It is important that HRM departments and HRD managers in schools offer organisational facilities for teachers. These facilities should focus not only on the traditional formal training activities, but also on creating opportunities for participation in social networks. This study indicates that, particularly, participation in intra- and extra-organisational social networks enhances occupational expertise. Managers can stimulate participation in these social networks by providing enough social support. Originality/value: Although teachers' professional development is increasingly perceived as being important in school settings, until now little empirical research has been available that investigates the relationship between organisational factors, TPD, and occupational expertise. (Contains 1 figure and 3 tables.)