Both direct and multistep reactions, involving the application of carbonyl compounds, e. g. oxoacids, phthalimides, 2-iodobenzamides or acylhalides, have been developed as novel synthetic routes for the preparation of 3- substituted 2,3-dihydro-1H-isoindol-1-ones, which are reviewed here. Alternatively, reductive or acid-catalyzed rearrangements of certain heterocycles lead to the formation of 3-substituted isoindolones. Asymmetric syntheses too have been described.