The aim of this work was to analyze and explain the demographic transition in the Republic of Croatia. The demographic transition is the process of transforming the traditional into a modern type of population reproduction, and in the Republic of Croatia began in 1880s. It is divided into 3 stages: the pre-transition phase, the demographic transition phase and the post-transition phase. In the following section, we look at the impact of demographic transitions on population changes, migration and the consequences of transition on the labor market, consumption and savings, and the pension system. This was followed by a chapter highlighting the main demographic trends in the European Union. The work concludes with a presentation of the projections of demographic trends in the Republic of Croatia for the period 2011-2051 and for the European union for the period 2015-2080. The Republic of Croatia is in an unfavorable demographic situation caused by a decline in population, more deaths than birts, demographic aging, an inbalance in age structure and negative migration. Predictions do not indicate that the demographic picture of Croatia could change for the better.