This master's thesis deals with the conditions that prevailed at the Italian-Yugoslav border in the period from 1929 to 1941 in the area of Rijeka and Sušak. This period coincides with the time when the former country was renamed the Kingdom of Yugoslavia. Since the Kingdoms of Italy and Yugoslavia were in strained diplomatic relations for most of the interwar period, it can be assumed that the activities and the need to control the state border were at a high level. This required special attention in defense, security and intelligence policy in both countries in the area of Rijeka and Sušak. The research was conducted through the perspective of microhistory, that is, the history of everyday life. In order to consolidate its territorial expansion, the Kingdom of Italy conducted an active defense policy along the border with Yugoslavia. The defense policy included the organization and investment in the army, defensive fortifications and frequent military maneuvers along the border. The second point was the intelligence and counterintelligence work of Italy and Yugoslavia. Both Kingdoms invested a great deal of financial resources in espionage and the prevention of foreign enemy espionage. Despite the great effort to secure the border, there are still data on the illegal crossings of various people across the border. Some of the most frequently mentioned defectors were Istrian refugees, opponents of political regimes, both in Italy (anti-fascists) and in Yugoslavia (Ustashas, communists, etc.). Illegal border crossings included smugglers who illegally transported trade goods, banned books and newspapers, people, weapons, ammunition, etc. Nevertheless, the citizens of the cities of Rijeka and Sušak had to live their lives. Many people living near the border had their own border card, which could not be issued to all people. Border cards were issued mostly to merchants, schoolchildren and workers who had to cross the border to get to work. The life of the citizens of Rijeka and Sušak and their surroundings will be discussed in order to explain the situation at the border between the Kingdom of Italy and Yugoslavia. The historical documentation that was used for the purpose of writing this master's thesis is located in the Croatian State Archives in Zagreb.