Teachers' professional development is not only important for teachers, also for schools' development. This study aims to explore teachers' engagement in communities of practice in schools and their views on the most effective professional development approach that they had experienced. The participants were 16 teachers from five schools in two states in Malaysia. The data was generated through semi-structured interviews. The analysis was done using thematic analysis, using Nvivo as a tool. The findings indicate that although for these teachers, attending courses, training and seminars helped them to gain new knowledge and related skills, their involvement in informal learning communities was significantly more meaningful for their professional development. This paper discusses the implications of this finding on the implementation of professional development currently being practiced in the Malaysian education system.