Prova tipográfica (In Press) ; Cesium iodide properties, both in the bulk and on (110) and (100) surfaces, are studied using Density Functional Theory. The bulk lattice constant, bulk modulus and elastic constants are in good agreement with the experimental values. The electronic band structure is also calculated, as well as the density of states. On the surfaces, relaxation of the atoms was performed, and the atomic geometry and electronic structure have been studied.