The aim of this work is to show what national security is, and what is the role of the police in the system of maintaining national security in the Republic of Croatia. The analysis of the role of the police in maintaining national security leads us to the fact that, using different sources of data and methods, we have come to the fact that the police, who protect their citizens and take care of their security, as well as the entire territory of their country, contribute greatly to the preservation of national security. The police in the Republic of Croatia is the main force for maintaining order and security. A police officer has the right to equal training and career development during his work. The development in the career of a police officer goes through different stages, from his schooling, training, education, as well as the very desire for the most precise work that leads to results. The Police of the Republic of Croatia cooperates with other international organizations, such as Europol, Interpol, NATO, and all in order to achieve better results in improving the preservation of national security in the country. The Republic of Croatia joined NATO later, unlike its neighboring countries Hungary and Slovenia, and Croatia, as well as Slovenia and Hungary, has similar methods for protecting the national security of its country. National security is the foundation of the state, its stability and the well-being of every sovereign society. In an ever-changing world, national security issues are becoming increasingly complex and challenging.