Optical microscopy is an important tool to analyse concrete and related materials (building stones, bricks …). Semitransparent thin sections as thin as 20 µm of concrete can be analysed by optical microscopy in brightfield or polarised light mode with or without tint plate. Additionally the thin sections can be impregnated with a fluorescent epoxy for fluorescence microscopy. Examination with fluorescence light microscopy gives information about the porosity of the material. Dense areas of the material appear dark green while porous areas appear yellowish. Brightfield microscopy reveals general information about the composition and structure of the material. Polarised light helps to identify crystallinity and composition of the minerals. Microscopical examination of concrete helps to assure quality and to evaluate durability and detoriation processes.