In my work, I want to highlight the importance of police cooperation both between the EU and the world. We live in the world of technology when we have the information at your fingertips. Fortunately, the rapid development of technology has brought with itself and faster communication between people miles away. Such a way is very important in police work. The co-operation of domestic and foreign police officers is done by posting to the police officers' mission, which has proved to be a high-quality experience transmitted by the police of one state to another in terms of the education and experience experienced by police officers in another country and bringing these experiences and knowledge into work in their countries. In addition to the missions performed by the attendance of police officers, co-operation is also carried out through Internet communication. Rapid communication between domestic and foreign police officers gives results in the prevention of criminal offenses, the arrest of persons wanted by a state, the suppression of crime related to cross-border smuggling, etc. Today, we are faced with a major migration problem where it is truly visible that without police co-operation it is not possible to perform the duties given to the police officers. Since the entry of the Republic of Croatia into the European Union on 1 March 2013, the possibilities of police extensions have been extended, which has greatly influenced the reduction of crime in the Republic of Croatia. It is very important for the European Union to be a region of freedom, security and justice and as such it is necessary to maintain cross-border cooperation in order to detect, prevent and investigate criminal offenses and capture their perpetrators. It is expected that the Republic of Croatia will become part of the Schengen area in the near future and will enhance the security of the EU's external borders, and Croatia has shown stable border control and security in migration flows that are still taking place. This is an essential part of FRONTEX; European Agency for the Management of Operational Cooperation at the External Borders of the Member States of the European Union.