Ion (Greek: Ἴων) is a play by Euripides, probably composed around 412BC. The title character is the son of Apollo, by Creusa daughter of King Erechtheus of Athens. Abandoned at birth, his recognition by his mother in adulthood provided a theme that would influence the later New Comedy.
Free online texts
Gutenberg: Ίων, Greek text. Multiple formats.
Internet Archive: The Ion of Euripides. Greek text with English translation. by A.W. Verrall (1890). Multiple formats.
Internet Classics Archive: Ion, translated by Robert Potter. HTML and TXT formats.
Loebulus: L012 - Euripides -- Euripides IV: Ion. Hippolytus. Medea. Alcestis. Greek and English parallel text. Loeb edition, PDF format.
Poetry in Translation: Ion, translated by George Theodoridis. Multiple formats.
University of Adelaide (Internet Archive): Ion, translated by Robert Potter. Multiple formats.
Gutenberg: Euripides and His Age, by Gilbert Murray.
History of Ancient Greece: Euripides at War, podcast by Ryan Stitt.
Wikipedia: Ion (play)
The Great Conversation: Further reading at Tom's Learning Notes
A.E. Haigh: The Tragic Drama of the Greeks (1896).
Ancient Greek resources: Learn to read Greek classics in the original.
Bloom's Western Canon: Ion is listed.