Several examples of industrial systems for gas-liquid chemical reaction with crystal precipitation are reviewed together with a particular focus on the means of predicting and controlling the physical form of the product. Specifically, a recent population balance analysis of crystallization coupled with the gas-liquid mass transfer model to predict the concentration and mixing rate dependencies of precipitate crystal size distributions is described. Secondary processes of particle agglomeration and disruption are also examined in terms of the effect of reactor fluid dynamics. Finally, different types of gas-liquid reactor are compared and design considerations summarised.