Porous calcium carbonate particles were synthesized by adding solutions of Ca 2+ to solutions of CO 3 2− containing polymeric additives. Under optimized conditions welldefined aggregates of the anhydrous polymorph vaterite formed. A typical sample of these micrometer-sized aggregates had a pore volume of 0.1 cm 3 /g, a pore width of ∼10 nm, and a specific surface area of ∼25−30 m 2 / g. Only one mixing order (calcium to carbonate) allowed the formation of vaterite, which was ascribed to the buffering capacity and relatively high pH of the CO 3 2− solution. Rapid addition of the calcium chloride solution and rapid stirring promoted the formation of vaterite, due to the high supersaturation levels achieved. With xanthan gum, porous and micrometer-sized vaterite aggregates could be synthesized over a wide range of synthetic conditions. For the other food grade polymers, hydroxypropyl methylcellulose (HPMC), methylcellulose (MC), and sodium carboxyl methylcellulose, several intensive and extensive synthetic parameters had to be optimized to obtain pure vaterite and porous aggregates. HPMC and MC allowed well-defined spherical micrometer-sized particles to form. We expect that these spherical and porous particles of vaterite could be relevant to model studies as well as a controlled delivery of particularly large molecules.