This is a review on the feasibility of monolithic porous supports in biocatalysis carried out in a continuous flow system. It discusses factors affecting the efficiency and stability of enzyme immobilisation, kinetic parameters of enzyme processes carried out inside a monolith, biocatalysis in single and two-phase systems, and cascade reactions including cofactor regeneration. It also covers materials engineering (monolith types) and issues related to the flow of reactants through the monolith (chemical engineering). Emphasis is placed on the fact that the application of (bio)catalysis improves selectivity and atom economy, thus lowering the E factor. However, biocatalysts need to be employed in a reactor, which can aid further improvement towards green chemistry goals. The application of enzymes in flow chemistry has been shown to lead to higher space time yields (STYs) compared to batch reactions. In particular, with monolithic reactors a drastic decrease in volume and thus solvent can be achieved. By immobilising very high densities of enzymes directly on the monolith, reaction times dwindle, improving STYs. The small reaction volumes enable excellent heat transfer, helping to save energy. The underlying principles of monolithic flow reactors and their application in mono- and bi-phasic biocatalytic systems will be examined.@en