This review highlights selected examples of photochemical transformations in microflow reactors. The main advantages of microflow reactors over conventional batch systems are superior light penetrations, controlled reaction times, precise temperature control and removal of photoproducts from the irradiated area. These features typically result in higher conversions or yields, improved selectivity, enhanced energy efficiencies and reductions of solvent volumes and consequently waste. Different types of homogeneous and heterogeneous reactions are presented, showing the superiority of microflow photochemistry over batch processes.