Hajdú-Bihar (; ) is an administrative county (comitatus or megye) in eastern Hungary, on the border with Romania. It shares borders with the Hungarian counties Szabolcs-Szatmár-Bereg, Borsod-Abaúj-Zemplén, Jász-Nagykun-Szolnok and Békés. The capital of Hajdú-Bihar county is Debrecen. Together with Bihor County in Romania it constitutes the Biharia Euroregion.