Exchangeable cations in zeolites are distributed over the available sites so as to minimize the energy of the unit cell. Site preferences can be adequately predicted by EEM calculations. Cation-lattice interactions as well as cation-cation repulsions have to be taken into account. In faujasites these repulsions disfavour simultaneous occupancy of adjacent sites I and I‘; I‘ and I‘ on opposite sites of an empty site I and add an additional component to the activation energy for migration of large alkali cations in the supercages. The coordination of Cu²⁺ is of low symmetry, but can be adequately described in the angular overlap model theory. The properties of the lattice oxygens are dependent on the structure type. This is translated in the charge transfer bands and in the EPR parameters of Cu²⁺. Low silica zeolites are especially suited for stabilization of small ionic clusters, mainly because of the high negative charge of the lattice and not so much for geometrical reasons.