Arsinoe III Philopator was Queen of Ptolemaic Egypt in 220 – 204 BC. She was a daughter of Ptolemy III and Berenice II and spouse of her brother Ptolemy IV. She was the first Ptolemaic queen to bear her brother's child.

The Ptolemaic Kingdom or Ptolemaic Empire was an Ancient Greek polity based in Egypt during the Hellenistic period. It was founded in 305 BC by the Macedonian general Ptolemy I Soter, a companion of Alexander the Great, and ruled by the Ptolemaic dynasty until the death of Cleopatra VII in 30 BC. Reigning for nearly three centuries, the Ptolemies were the longest and final dynasty of ancient Egypt, heralding a distinctly new era for religious and cultural syncretism between Greek and Egyptian culture.