Despite more than 20 y of awareness of the importance of calcium to health, U.S. calcium intakes remain suboptimal. Fortification of foods with shortfall nutrients is probably the optimal strategy for dealing with widespread nutrient deficiencies, as it has the best chance of reaching the population segments most at risk, as contrasted with attempts at changing individuals' food choices or relying on voluntary supplement taking. Given the wide array of potential calcium fortificants and fortification levels, there is not much to guide manufacturers interested in improving the nutritional value of their products. In this review, we assemble the calcium salts/complexes that have been used or proposed for use as fortificants and describe certain of their measured characteristics that relate to incorporation into foods, particularly what is known of their absorbability. The calcium salts most commonly used as supplements or fortificants exhibit similar absorbability when tested in pure chemical form. Choice of salt will depend mainly upon cost, compatability with the manufacturing process, and consumer acceptability. However, interaction with food, tablet, or beverage matrices can degrade intrinsic absorbability substantially. As a consequence, each product must be explicitly tested to establish the degree to which its calcium is available to consumers.