Omurtag  is a town at the eastern foot of Stara Planina in northeastern Bulgaria, part of Targovishte Province. Situated at 525 m above sea level, it has 11,124 inhabitants as of September 2005.

The area around the modern town has been inhabited since the Neolithic. Part of Justinian I's defensive system in the 6th century, the region gained importance as part of the First Bulgarian Empire due to the proximity to the capitals Pliska and Preslav and the passes of Stara Planina.

The first written evidence of the modern town date from the 17th century, when it was mentioned as the kaza centre Osman Pazar in Ottoman tax registers. The settlement was a centre of craftsmanship and trade. Osman Pazar was liberated from Ottoman rule on 27 January 1878 by Russian troops under Johann Casimir Ehrnrooth during the Russo-Turkish War of 1877-78. Most of the Turkish inhabitants of the town left to be replaced by Bulgarians from around Tran and Kyustendil. Omurtag acquired its present name in 1934, named after Bulgarian khan Omurtag.