Monolithic stationary phases provide high rates of mass transfer at low pressure drops and enable much faster separations. Experimental data from published H versus u plots obtained with monolithic columns are compiled with an emphasis on the mass tranfer (C term of the van Deemter equation). Silica-based monoliths of the C18 Chromolith type exhibit a very low C value that does not vary too much within a wide range of flow rates. The C term is a function of retention, temperature, molecular weight of the solute and mesopore size. Silica-based monoliths of capillary format exhibit a slightly higher C value which slightly increases with increasing flow rates. The key parameter is the through-pore size/skeleton size ratio. Experimental data on polymer-based monoliths retrieved from the literature mostly concern acrylate-based material in a capillary format. Due to the unique character of every column the scatter of published C values is wide. The observed C term are higher than those observed with silica monoliths and increase quite linearly with the flow rate. Low-density polymers exhibit better performances than high-density polymers. The majority of HETP versus u plots are drawn from the peak width at half height. Accurate data should be acquired through the second moment of the peak. Some equations for C have been derived. An equivalent dispersion particle diameter is a measure of band broadening in the mesopores. Mass transfer in silica monoliths is well accounted by the theory developed by Guiochon et al.