Highly porous polymers (polyHIPEs) have been prepared by the photopolymerization of high internal phase emulsions (HIPEs) with varying ratios of thiol and acrylate monomers. The resulting polymers have a nominal porosity of 80%, and are seen to have a well-defined, interconnected pore morphology, with average pore diameters ranging from 30 to 60 μm. The polyHIPE polymers have been shown using a colourimetric (Ellman's) assay to contain residual thiols which are reactive towards a range of (meth)acrylates (hexafluoroisopropyl acrylate, fluorescein O-acrylate and poly(ethylene glycol) methyl ether methacrylate). Functionalization was explored using thermally- and UV-initiated radical-mediated “click” reactions and an amine-catalysed Michael addition reaction. The extent of functionalization was investigated qualitatively and quantitatively using a range of techniques (solid state NMR spectroscopy; FTIR spectroscopy; X-ray photoelectron spectroscopy (XPS); observation of fluorescence); high levels of conversion (up to 90–95%) were observed for the thermally-initiated radical reaction and the Michael reaction.