CAMEO is a modular expert system, a computer program that predicts the products of organic reactions given starting materials, reagents and conditions. The analyses primarily feature mechanistic reasoning and have been extended to cover most of the major classes of organic reactions (currently: Basic/Nucleophilic, Acidic/Electrophilic, Electrophilic Aromatic Substitution (EAS), Radical, Heterocyclic, Pericyclic, Oxidative/Reductive, Carbene, Pd Organometallic and Photochemical). An important aspect of the project has been to clearly define the logic behind accurate prediction of products and to simultaneously search for organizing principles governing organic reactivity.