Sudak (Ukrainian and Russian: Судак; Crimean Tatar: Sudaq; Greek: Σουγδαία; sometimes spelled Sudac or Sudagh) is a city, multiple former Eastern Orthodox bishopric and double Latin Catholic titular see. It is of regional significance in Crimea, a territory recognized by most countries as part of Ukraine but annexed by Russia as the Republic of Crimea. Sudak serves as the administrative center of Sudak Municipality, one of the regions Crimea is divided into. It is situated 57 km (35 mi) to the west of Feodosia (the nearest railway station) and 104 km (65 mi) to the east of Simferopol, the republic's capital. Population: 16,492 (2014 Census).

A city of antiquity, today it is a popular resort, best known for its Genoese fortress, the best preserved on the northern shore of the Black Sea.

The date and circumstances of the city's foundation are uncertain. The first written reference to the city dates to the 7th century (in the Ravenna Cosmography), but later local tradition places its foundation in 212 CE, and archaeological evidence supports its foundation in Roman times. The city was in all likelihood founded by the Alans, as its name in Greek sources, Sougdaia is a cognate of the adjective sugda ("pure, holy") or derives from the word sugded/sogdad in the Ossetian language.

In the early Middle Ages, the city appears to have been under very loose Byzantine control, like other cities in the region. Archaeological remains indicate considerable construction activity near the shore in the 6th century. Under Byzantine influence, the city was subject to Christianization, and became the seat of a bishopric under the Patriarch of Constantinople, attested for the first time in the Second Council of Nicaea in 787. Although a Greek-speaking population was probably settled in the city, the area remained dominated by the Alans: a 9th-century hagiography of Apostle Andrew places "Upper Sougdaia" elsewhere, between Zichia and the Cimmerian Bosporus, "in the land of the Alans", while the hagiographer of Constantine the Philosopher mentions the tribe of Sougdoi, situated between the Iberians and the Crimean Goths, which the historian Francis Dvornik identifies as the Alans.

The period between the 8th and 11th centuries is obscure, but the available evidence points to a sharp decline in Sougdaia's fortunes. Archaeological evidence shows that the 6th-century constructions were abandoned in the 8th/9th century, while later Russian legends (probably apocryphal) claim that the city was captured by the Rus' chieftain, Bravlin, at around the same time. Byzantine control lapsed, and the city probably came under Khazar suzerainty thereafter, which lasted until the early 11th century. In the early 10th century, the local see was promoted to an archbishopric.

The 11th–14th centuries represent a period of prosperity for the city, as shown in archaeological evidence of renewed activity both in the harbour as well as the hinterland and the area of the citadel. It became an important location for trading on the Silk Road in the 12th and 13th centuries, as a terminus for Black Sea trade. The 14th-century Arab traveller Ibn Battuta even compares its harbour with that of Alexandria. The 13th-century chronicler Ibn al-Athir writes of it as the "city of the Qifjaq from which (flow) their material possessions. It is on the Khazar Sea. Ships come to it bearing clothes. The Qifjiqs buy from them and sell them slaves. Burtas furs, beaver, squirrels ..."

By the mid-11th century, Sougdaia had returned to Byzantine control, probably following the defeat of the Khazar warlord Georgius Tzul in 1016. An inscription of 1059 mentions Leo Aliates, "strategos of Cherson and Sougdaia". By the end of the century, however, the city passed under Cuman control, which lasted until the 13th century. In c. 1222 the Seljuk Turks besieged it, followed by destructive raids by the Mongol Empire in 1223 and 1238. Finally, in c. 1249 the city came under the control of the Mongol Golden Horde, although it retained considerable autonomy. Contemporary sources place its population at the time to 8,300, including Greeks, Alans, Mongols, Armenians, Latins, and Jews.

Under Tatar rule, the city was governed by the notables of the city and the 18 villages surrounding it. In the Greek sources they are mentioned by the Byzantine title sebastos, while the Latin sources use the Latinized Greek term proti ("first men"). Sometime between 1275 and 1282, the local see, which after being united with Phoulloi in the late 11th century was known as Sougdophoulloi, was raised to the status of a metropolitan see.