The theory of thermal explosion, first expressed in quantitative forms by Semenov and Frank-Kamenetskii has been extensively developed in recent years and provides a model for self-heating and explosion in certain gas reactions, explosives, propellants and unstable chemical substances. The present paper outlines the application of the simple 'stationary state' form of the model to the self-heating and ignition, by oxidation, of organic materials. Application in this area is often near the borderline of validity of the theoretical model but nevertheless is of great practical value in treating problems of self-heating and ignition of organic materials in storage and transport. The applications considered include the ignition of cellulosic materials, activated carbon, and mixtures of vegetable oils and sawdust intended to simulate commodities such as oilseed meals, oiled textiles and fishmeal. The paper is principally concerned with experimental results and their interpretation with the aid of the model. Theoretical results needed will be stated without derivation but can be amplified in discussion as necessary.