The role of a facilitator is key to the effective establishment and sustainment of Communities of Practice (COP). This paper presents a taxonomy of facilitation tasks that have to be carried out to support various COP processes that take place during the different stages in a COP's life-cycle. Inspired by facilitation research in the area of Group Support Systems (GSS), we identified 33 facilitation tasks. These tasks are grouped into internal facilitator roles (Information Source, Inspirator, Guide) and external facilitator roles (Information Source, PR Manager, Investigator). The COP facilitation task taxonomy can serve as a basis for training COP facilitators, as a guide for COP facilitators to prepare for and assume their role, as a starting point for developing tool support for COP facilitators, and finally as a research instrument to study COP facilitators in the field or devise experimental treatments focusing on facilitation of large online groups.