The genetic management of small populations, irrespective of the objective pursued, it is conditioned by their census. Actually the distinction between conservation and selection programmes tends to vanish because in both types of programmes attention should be paid to the increase of inbreeding and to the maintenance or improvement of some traits of interest. To maintain genetic diversity the criterion to follow is to maximize the effective population size. For this purpose several simple rules have been developed during the last decades although there exist also a sophisticated solution, probably optimal. For selection programmes there are also simple rules and an optimal solution although now the desired genetic progress should be included. The design of optimal mating systems, although it presents more problems from a theoretical point of view, it has also a reasonable practical solution.