We examine country differences in teachers’ participation in professional development (PD) and collaboration and explore which factors explain differences among countries. We show that PD participation and teacher collaboration differ considerably among countries and that the levels of PD participation and teacher collaboration are weakly related to one another at both the country and school levels. Although higher overall accountability pressure explains some PD participation gaps, most differences remain unexplained. Regarding teacher collaboration, no single factor accounts for variations across all countries. However, teacher characteristics, particularly the proportion of full-time employed teachers, account for collaboration gaps among specific countries.