Cambodia’s teacher professional development (PD) system is at a crossroads. There is a growing realization that the lower than expected learning outcomes in Cambodia are directly related to lower than desirable classroom teaching. To respond to this reality, Cambodia aims to put in place improved systems for pre-service teacher preparation (moving to a 12+4 system and introducing a new Bachelor of Arts in Education (BA [Ed.]) degree, intensive upgrading of existing teachers, and continuous professional development and mentoring. A working group organized by the Teacher Training Department is bringing together stakeholders to assist in the design and implementation of an improved in-service training (INSET) system. The present document aims to bring together pertinent information and evidence on effective continuous professional development (CPD) to support the work of this group.