In 1993, the Organization for Economic Cooperation and Development/Nuclear Energy Agency first convened the Working Group on the Physics of Plutonium Recycle (WPPR) (now renamed the Working Party on the Physics of Plutonium Fuels and Innovative Fuel Cycles). Since its inception, the WPPR (whose task has now been expanded to include innovative fuel cycles) has published six volumes of detailed results from analyses of plutonium fuel in pressurized water reactors and fast reactors. A seventh volume on the physics of plutonium fuel in boiling water reactors is in preparation. The analyses have been mostly in the form of theoretical benchmark exercises for situations beyond current experience, for which multinational contributions provide a basis for comparison of diverse calculational methods and nuclear data libraries. The overall activities of the WPPR are reviewed and summarized.