Greece and Italy enjoy special and very strong bilateral diplomatic relations. Modern diplomatic relations between the two countries were established right after Italy's unification. During the second world war, Italy under Mussolini waged war against Greece. Today relations are again regarded as cordial. The two states cooperate in fields of energy, security, culture and tourism, and are major trading partners, both in exports and imports. Greeks and Italians often exchange the phrase "una faccia, una razza", meaning "one face, one race". Greece and Italy share strong cultural ties which date back to Antiquity.

Greece and Italy share common political views about the Balkans, the Mediterranean Basin, and the world, and are leading supporters of the integration of all the Balkan nations to the "Euro-Atlantic family", and promoted the "Agenda 2014", which was proposed by the Greek Government in 2004 as part of the EU-Western Balkans Summit in Thessaloniki, to integrate the Western Balkan nations into the EU by the year 2014, when Greece and Italy assumed the rotating Presidency of the European Union for the first and second halves of 2014, respectively.

The two countries are European Union, NATO and United Nations member states, and cooperate in many other multilateral organizations, such as the Organization for Security and Co-operation in Europe, the Organisation for Economic Co-operation and Development, the World Trade Organization, and the Union for the Mediterranean, while at same time they are promoting closer diplomatic relations and cooperation with other key countries and organizations, such as the United States, Israel and the African Union.

Relations between the regions of present-day Greece and Italy date back to ancient times. As early as the 8th century BC, Greek settlers founded colonies in the south of the Italian peninsula (later known as Magna Graecia). The Greeks brought urban lifestyles, their religion, winegrowing and their alphabet to southern Italy. Even after the Roman conquest of Greece in the 2nd century BC, the cultural influence of the Greeks on Rome remained very significant. The Romans admired Greek art and philosophy and adopted many elements of Greek culture, for example in architecture and literature. At the same time, Rome and Greek-speaking empires expanded their political interests in their respective territories. In the period that followed, the so-called Greco-Roman culture and civilization developed, combining elements of both ancient worlds. Cities such as Naples and Taranto in Italy remained Greek in character and predominantly Greek-speaking for a long time, even under Roman rule. The Greek influence on ancient Rome was evident in many ways in art, culture, and architecture. Many members of the Roman elite spoke Greek, and Roman authors (such as Cicero) showed great admiration for Greek philosophy.

After the collapse of the Western Roman Empire (5th century), the Greek-speaking eastern part of the empire – the Byzantine Empire – remained intact for almost a millennium. Byzantium also ruled over parts of Italy at various times, including southern Italy in the 6th–8th centuries. In parts of southern Italy (Calabria and Apulia), Greek-speaking communities persisted into the Middle Ages, partly as remnants of antiquity and partly due to Byzantine immigration. These Griko dialects are still spoken today in some villages in Apulia and Calabria. During the Middle Ages, however, the Byzantines and the rising Italian powers were also rivals. From the 13th century onwards, the Republic of Venice gained important strongholds in Greece. Venice ruled over the Ionian Islands for several centuries (from the 14th to the late 18th century). At times, Venetian or Genovese nobles also controlled mainland areas in Greece (such as the Latin Empire after the Fourth Crusade in 1204). Venice played an important role as a colonial power, particularly in Crete (1211–1669) and Cyprus (1474–1571). The Venetian presence left lasting traces in Greece, for example in the form of fortifications and cultural influences on the Ionian Islands. At the same time, close contacts existed between Italian and Greek port cities through Mediterranean trade.

However, from the 15th century onwards, the Ottoman Empire replaced Byzantium as the dominant power in Greece, increasingly pushing back Italian spheres of influence. Nevertheless, cultural exchange remained lively: after the Ottoman conquest of Constantinople in 1453, many Byzantine Greek scholars fled to Italy, bringing with them valuable ancient manuscripts and their knowledge. These scholars (such as Bessarion and John Argyropoulos) made a significant contribution to the Renaissance in Italy by promoting the study of Greek antiquity and transmitting ancient knowledge to the West. Cultural exchange intensified during this period: Italian humanists learned Greek, translated ancient Greek works into Latin, and the first printed editions of Greek classics appeared in Italy. In this way, Greek intellectuals in exile laid important foundations for science and culture in the Italian Renaissance (see Greek scholars in the Renaissance).

Greece (which had gained its independence in 1830) and Italy established diplomatic relations in 1861, immediately upon Italy's unification. Italian philhellenes had contributed to the Greek independence, such as the jurist Vincenzo Gallina, Annibale Santorre di Rossi de Pomarolo, Count of Santarosa, and Giuseppe Rosaroll.

Throughout the 19th century, Italian philhellenes continued to support Greece politically and militarily. For example, Ricciotti Garibaldi led a volunteer expedition (Garibaldini) in the Greco-Turkish War of 1897. A group of Garibaldini, headed by the Greek poet Lorentzos Mavilis, fought also with the Greek side during the Balkan Wars.