Two in situ process analytical technologies were used to investigate a cocrystallization process: a focused beam reflectance measurement probe and a video probe. The cocrystallizations were conducted batch-wise in a stirred thermostatted vessel with carbamazepine and nicotinamide. The experiments were started in three domains of the phase solubility diagram. When carbamazepine crystals were also formed, a solution mediated phase transition from carbamazepine crystals towards cocrystals was initiated by the addition of the cocrystallizing agent (nicotinamide crystals). As the carbamazepine crystals and the carbamazepine/nicotinamide cocrystals exhibit prism-like and needle-like habits, respectively, it was possible to discriminate between them with the two sensors. The mechanisms involved in the solution mediated phase transition were investigated.