Monolith reactors are emerging as an attractive alternative for gas-liquid-solid reactor applications. The use of monolithic catalysts in new reactors as well as in retrofit designs should be based on an optimal choice of monolith geometry and operating conditions. In this contribution, we illustrate through fundamental modeling of the transport-kinetic interactions in a monolith catalyst how such an optimal design may be evolved. We also highlight the potential benefits a monolith catalyst has as compared to a pellet-based trickle bed reactor. (C) 2003 Elsevier Ltd.