The concept of population migration (mechanical movement) means the primary mobility or spatial mobility of the population. The concept of population mobility is wider than the notion of migration, because migration is the spatial mobility of the population and as such is only one form of total population mobility. Migration in the wider sense is considered to be any form of relocation, temporary or permanent change of place of residence, while migration in the narrow sense relates only to permanent changes in the place of residence. The Republic of Croatia is among the European countries where the population has not been renewed for several decades, but is declining, both in total and in some generations. Increased aging or increasing the number of the old people's population while reducing the reproductive base, the number of young people, further increases the imbalance among individuals for economic and social development of key functional age groups and leads to demographic inability.