Demetrius Phalereus ( - died approximately 280 BC) was an Athenian orator and one of the first Peripatetics. Demetrius wrote extensively on the subjects of history, rhetoric, and literary criticism.

From 317 BC to 307 BC he was governor of Athens, serving under Cassander. When Demetrius I of Macedon took Athens Demetrius Phalereus was overthrown, and he fled to Egypt. In Egypt Demetrius met Ptolemy I, and it is thought that it was his suggestion that inspired the creation of the Library of Alexandria. Demetrius went into exile a second time on the accession of Ptolemy Philadelphus, and he died soon afterward.