An overview of the state of the art and future trends in vapour phase oxidation and ammoxidation of substituted methyl aromatics and heteroaromatics is presented. The topics mainly contain the conversion of methoxytoluenes, chlorotoluenes and methylpyridines to the corresponding aldehydes and nitriles by vapour phase reaction using V-containing catalysts. Steric and electronic effects of various substituents in combination with acid-base properties of catalyst surfaces on the catalytic performance are discussed; common features and differences in mechanistic steps are demonstrated. The optimum catalyst composition for vapour phase partial oxidation to aldehydes is quite different from that for vapour phase partial ammoxidation to nitriles. (C) 2000 Elsevier Science B.V. All rights reserved.