Calcium carbonate is one of the most abundant materials present in nature. In this book, the characterization of surface properties of calcium carbonate are reviewed, particularly, the Washburn method is described in detail. The effect of natural and synthetic macromolecules on the structure of calcium carbonate is described as well. The third chapter highlights the general criteria for the application of vaterite (an artificially prepared compound, which has the least thermodynamic stability among the three crystalline polymorphs of calcium carbonate) for biomedical applications and the science of its structural modification towards achieving tunable solubility. The final chapter examines the porous calcium carbonate cores as templates for preparation of peroral proteins delivery systems and the influence of ionic composition of intestinal medium on the structure and morphology of carbonate cores and release profiles of model and therapeutic proteins.