The Republic of Ragusa was an aristocratic maritime republic centered on the city of Dubrovnik (Ragusa in Italian and Latin; Raguxa in Venetian) in South Dalmatia (today in southernmost Croatia) that carried that name from 1358 until 1808. It reached its commercial peak in the 15th and the 16th centuries, before being conquered by Napoleon's French Empire and formally annexed by the Napoleonic Kingdom of Italy in 1808. It had a population of about 30,000 people, of whom 5,000 lived within the city walls. Its motto was "Non bene pro toto libertas venditur auro", a Latin phrase which can be translated as "Liberty is not well sold for all the gold".

Originally named Communitas Ragusina (Latin for "Ragusan municipality" or "community"), in the 14th century it was renamed Respublica Ragusina (Latin for Ragusan Republic), first mentioned in 1385. It was nevertheless a Republic under its previous name, although its Rector was appointed by Venice rather than by Ragusa's own Major Council. In Italian it is called Repubblica di Ragusa; in Croatian it is called Dubrovačka Republika (Croatian pronunciation: [dǔbroʋat͡ʃkaː rěpublika]). It is generally known in historiography as the Republic of Ragusa.

The Slavic name Dubrovnik is derived from the word dubrava, "an oak grove," by a folk etymology. The name Dubrovnik of the Adriatic city is first recorded in the Charter of Ban Kulin (1189). It came into use alongside Ragusa as early as the 14th century. The Latin, Italian and Dalmatian name Ragusa possibly derives its name from Lausa (from the Greek ξαυ: xau, "precipice"); it was later altered to Rausium, Rhagusium, Ragusium or Rausia (even Lavusa, Labusa, Raugia and Rachusa) and finally into Ragusa. Another theory is that the term "Ragusa" derivatives from or is related to Proto-Albanian *rāguša meaning 'grape' (compare Modern-Albanian rrush (meaning "grape")), according to V. Orel.

The Republic ruled a compact area of southern Dalmatia – its final borders were formed by 1426 – comprising the mainland coast from Neum to the Prevlaka peninsula as well as the Pelješac peninsula and the islands of Lastovo and Mljet, as well as a number of smaller islands such as Koločep, Lopud, and Šipan.

In the 15th century the Ragusan republic also acquired the islands of Korčula, Brač and Hvar for about eight years. However they had to be given up due to the resistance of local minor aristocrats sympathizing with Venice, which was granting them some privileges.

In the 16th century the administrative units of the Republic were: the City of Ragusa (Dubrovnik), counties (Konavle, Župa dubrovačka – Breno, Slano – Ragusan Littoral, Ston, Island of Lastovo, Island of Mljet, Islands of Šipan, Lopud and Koločep) and captaincies (Cavtat, Orebić, Janjina) with local magistrates appointed by the Major Council. Lastovo and Mljet were semi-autonomous communities each having its own Statute.

According to the De Administrando Imperio of the Byzantine emperor Constantine VII Porphyrogennetos, the city was founded, probably in the 7th century, by the inhabitants of the Greek city of Epidaurum (modern Cavtat) after its destruction by the Avars and Slavs c. 615. Some of the survivors moved 25 kilometres (16 miles) north to a small island near the coast where they founded a new settlement, Lausa. It has been claimed that a second raid by the Slavs in 656 resulted in the total destruction of Epidaurum. Slavs settled along the coast in the 7th century. The Slavs named their settlement Dubrovnik. The Byzantines and Slavs had an antagonistic relationship, though by the 12th century the two settlements had merged. The channel that divided the city was filled, creating the present-day main street (the Stradun) which became the city centre. Thus, Dubrovnik became the Slavic name for the united town. There are recent theories based on excavations that the city was established much earlier, at least in the 5th century and possibly during the Ancient Greek period (as per Antun Ničetić, in his book Povijest dubrovačke luke). The key element in this theory is the fact that ships in ancient time traveled about 45 to 50 nautical miles (83 to 93 km; 52 to 58 mi) per day, and mariners required a sandy shore to pull their ships out of the water for the rest period during the night. An ideal combination would have a fresh water source in the vicinity. Dubrovnik had both, being halfway between the Greek settlements of Budva and Korčula, which are 95 nautical miles (176 km; 109 mi) apart.

During its first centuries the city was under the rule of the Byzantine Empire. The Saracens laid siege to the city in 866–867; it lasted for fifteen months and was raised due to the intervention of Byzantine Emperor Basil I, who sent a fleet under Niketas Ooryphas in relief. Ooryphas' "showing of the flag" had swift results, as the Slavic tribes sent envoys to the Emperor, once more acknowledging his suzerainty. Basil dispatched officials, agents and missionaries to the region, restoring Byzantine rule over the coastal cities and regions in the form of the new theme of Dalmatia, while leaving the Slavic tribal principalities of the hinterland largely autonomous under their own rulers. With the weakening of Byzantium, Venice began to see Ragusa as a rival that needed to be brought under its control, but an attempt to conquer the city in 948 failed. The citizens of the city attributed this to Saint Blaise, whom they adopted as their patron saint.