The Costoboci (^{[pronunciation?]}; Latin: Costoboci, Costobocae, Castabocae, Coisstoboci, Ancient Greek: Κοστωβῶκοι, Κοστουβῶκοι or Κοιστοβῶκοι) were an ancient people located, during the Roman imperial era, between the Carpathian Mountains and the river Dniester. The Costoboci invaded the Roman empire in AD 170 or 171, pillaging its Balkan provinces as far as central Greece, until they were driven out by the Romans. Shortly afterwards, the Costoboci's territory was invaded and occupied by Vandal Astingi and the Costoboci disappeared from history.

Mainstream modern scholarship locates this tribe to the north or north-east of Roman Dacia. Some scholars considered that the earliest known mention of this tribe is in the Natural History of Pliny the Elder, published ca. AD 77, as a Sarmatian tribe named the Cotobacchi living in the lower Don valley.. Other scholars have challenged this identification and have recognised the "Cotobacchi" as a distinct tribe.

Ammianus Marcellinus, writing in ca. 400, locates the Costoboci between the Dniester and Danube rivers, probably to the north-east of the former Roman province of Dacia. In his Geographia (published between 135 and 143 AD), the Greek geographer Ptolemy seems to indicate that the Costoboci inhabited north-western or north-eastern Dacia. In addition, some scholars identify the people called Transmontanoi (literally: "people beyond the mountains") by Ptolemy, located to the north of the Carpathians, as Dacian Costoboci. These Costoboci Transmontani, according to Gudmund Schütte, also inhabited the Dacian town of Setidava mentioned by Ptolemy, located by Schütte in the south-east of modern Poland.^{[undue weight? – discuss]}