Abstract The deliberate incorporation of additional process functions to enhance reactor performance has proved to be a fertile approach in developing novel reactors. In addition, the concept of these so-called multifunctional reactors offers a useful framework for reactor selection and classification. Two earlier classification schemes based on the underlying heat and mass transfer processes and the combination of reaction with various unit operations are reviewed. The utility of these conceptualisations in reactor analysis is illustrated using the Claus process and hydrogen cyanide synthesis as examples. A new taxonomy obtained by considering the phases participating in the reactor operation is proposed. The shortcomings of previous work on multifunctional reactors, primarily the absence of technical and economic comparisons with alternative reactor designs, are discussed. The potential for further improvements, especially those exploiting the spatial distribution of functionalties within the reactor and by using structured ‘multifunctional’ catalysts, is examined.