Háromszék (Three Seats; Romanian: Trei Scaune) was an administrative county (comitatus) of the Kingdom of Hungary.

Situated in south-eastern Transylvania, its territory is now in central Romania (in the counties of Covasna, Brașov, and Bacău).

The Carpathian Mountains formed its southern and eastern border.

In 1920, under the Treaty of Trianon, the county became part of the Kingdom of Romania under the name Trei Scaune.

After the Second Vienna Award of August 1940, the county was recreated with most of its historic territory as it became part of the Northern Transylvania territory of Hungary again until October 1944, towards the end of World War II.