A review. Within the German Tropospheric Research Program (TFS) numerous kinetic and mechanistic studies on the tropospheric reaction/degrdn. of the following reactants were carried out: .bul. oxygenated VOC, .bul. arom. VOC, .bul. biogenic VOC, .bul. short-lived intermediates, such as alkoxy and alkylperoxy radicals. At the conception of the projects these selected groups were classes of VOC or intermediates for which the atm. oxidn. mechanisms were either poorly characterized or totally unknown. The motivation for these studies was the attainment of significant improvements in our understanding of the atm. chem. oxidn. processes of these compds., particularly with respect to their involvement in photooxidant formation in the troposphere. In the present paper the types of exptl. investigations performed and the results obtained within the various projects are briefly summarized. The major achievements are highlighted and discussed in terms of their contribution to improving our understanding of the chem. processes controlling photosmog formation in the troposphere.