Justinian I was one of the most important rulers of the Byzantine State. Justinian, who joined the state administration from the time of his uncle Justin I, had the greatest goal after becoming the ruler to bring the Byzantine State back to its old borders. As a result of all these, he organized expeditions to North Africa, Italy and Spain. As a result of these expeditions, North Africa was completely dominated, Italy was partially captured and the southeast of Spain was captured. In order to protect his borders, Justinian also organized expeditions against the Slavs and Bulgarians who were constantly harming Byzantine lands, but he could not completely destroy them. Another state that had an important place in the foreign policy of the Justinian period was the Sassanids. The most important thing that shaped the Byzantine-Sassanid relations during this period was the attacks of the Sassanids on Byzantium. Since Justinian was more concerned with the West, he refrained from fighting the Sassanids. In this study, the foreign policy of the Justinian period will be explained.