The paper describes the living anionic polymerization of styrenes to homo- and diblock copolymers in continuous flow, using a microstructured mixing set-up (“microreactor”). Reaction times and experimental effort are significantly reduced compared to classical batch methods that often require stringent reaction conditions and strict drying of the apparatus by “break-seal” and “high vacuum” techniques. In continuous flow, residual impurities can be removed by purging the reactor with monomer and initiator solution before polymer samples are collected at the device outlet on a scale of up to 200 g · h−1. Facile molecular weight adjustment is achieved by variation of the flow rates of initiator or monomer solutions. The polymerization of styrene in THF and cyclohexane was studied with respect to control of molecular weight and polydispersity. Furthermore, diblock copolymers with different block lengths and low polydispersities, consisting of styrene- and 4-tert-butoxystyrene blocks were synthesized, employing a second micromixer for a delayed introduction of the additional monomer. All materials were investigated by NMR-spectroscopy, SEC/MALLS, and MALDI-TOF mass spectrometry, confirming narrow molecular weight distributions (MWDs; 1.09–1.25), molecular weights in the range of 500–70 000 g · mol−1, and complete end-functionalization. No dimerization due to side reactions that would occur in the presence of oxygen was observed, evidencing efficient shielding of the apparatus from environmental influences.