Ion of Chios was a 5th-century BCE Greek poet, dramatist, and prose author from the island of Chios. A contemporary and acquaintance of figures like Sophocles and Cimon, he was active in both Ionian and Athenian cultural spheres. He achieved success in Athenian dramatic competitions and died in Athens, likely during the Peloponnesian War.

He combined literary pursuits with philosophical interests, notably proposing a cosmological system in his prose work Triagmos. This work posited fire, earth, and air as fundamental principles, showing Pythagorean influence. His diverse, fragmentary works include tragedies such as Agamemnon and Teucer, dithyrambs, elegiac and lyric poetry, and possibly comedies. His significant prose includes the cosmological Triagmos and the memoir Epidemiai, which recorded anecdotes of his famous contemporaries.

Ion is significant for embodying the intellectual cross-currents of his era, blending Ionian speculative philosophy with Athenian public poetry. His Triagmos is a key fragment of pre-Socratic thought, and his Epidemiai was a valued biographical source. He is remembered as a polymath whose corpus illustrates the interconnected culture of the Classical Greek world.