This study explores the factors affecting firms’ decisions on how many types of products to produce (their ‘product scope’). A theoretical model is presented. The study then uses data for 2000–2012 to examine the role of supply-side factors in product scope decisions of Indonesian manufacturing plants. Larger plants, those in less competitive markets, those that utilise imported materials, and older plants tend to have wider product scopes. The effect of export intensity is not monotonic. Foreign ownership weakly corresponds to leaner product scope, while evidence on the role of productivity is less clear. The implications of the findings will be discussed.