Idrieus, or Hidrieus (Ancient Greek: Ἱδριεύς, romanized: Hidrieús; died 344 BC) was a ruler of Caria as a Satrap under the Achaemenid Empire.

Alongside his sister and wife Ada, he enjoyed the status of king or dynast by virtue of the powerful position he inherited from his predecessors of the House of Hecatomnus (the Hecatomnids).

Shortly after his accession he was required by the Persian king, Artaxerxes III Ochus, to provide arms and troops for the capture of Cyprus, a request with which he readily complied.

[6] Unlike Mausolus, Idrieus called himself 'Mylasan' (Ancient Greek: Ιδριεὺς Ἑκατόμνω Μυλασεὺς) in his inscribed dedications, emphasising his local roots.

[8] His sister shared his rule in a junior capacity throughout his life, and appeared alongside him in dynastic portraits at Mylasa, Tegea in the Peloponnese, and statues at Delphi dedicated by the people of Miletos in Caria.