Process for the manufacture of sodium carbonate crystals comprising: the addition of solid sodium carbonate (1) to an aqueous solution comprising sodium bicarbonate and sodium carbonate; the crystallization and the separation of sodium sesquicarbonate crystals; (B, C) the crystallization of sodium carbonate crystals, (E) the amount of sodium carbonate added being adjusted so that the crystallization of sesquicarbonate crystals can be carried out without preliminary evaporation of the aqueous suspension.