Due to high routine vaccination coverage, overall counts of diphtheria case have significantly declined in the Western Pacific Region recently. However, diphtheria is still prevalent in several countries and areas of the Region and remains a public health issue due to its high case fatality rate. This Field Guide for Preparedness and Response to Diphtheria Outbreaks in the Western Pacific Region is a reference resource for Member States to develop national guidelines adapted to their local context. Countries may also use this Guide to facilitate outbreak preparedness and public health responses to reduce morbidity and mortality due to diphtheria.