In this thesis, the author presented the security challenges that the Republic of Croatia needs to face after entering the Schengen area. The first part of the thesis, related to the Schengen area and the idea of „Europe without borders“, presents a historical background of the Schengen area's development and describes the base lines of the Schengen area: characteristics of it as an area without internal border controls and three systems that are important for maintaining security: Schengen Information System, Common Asylum System and Visa Information System. In the second part of the thesis, the author emphasizes the geopolitical, security and economic aspects of Croatia joining the Schengen area, whereby the stages of access and the challenges during the process of joining the Schengen area are first described, and then the effects of Croatia's accession to the Schengen area on Croatian economy, especially on tourism. In the third part of the thesis, the author pointed out some open questions about the Schengen area as an open area of free movement, such as security challenges (migration crisis, terrorism and the pandemic), after which he emphasized the new role of Croatia as a frontier towards the European Union, as well as the security challenges Croatia has to deal with (unauthorized migration, human trafficking, terrorist threats).