Lucius Aelius Stilo Praeconinus (; c. 154 – 74 BC), of Lanuvium, is the earliest philologist of the Roman Republic. He came from a distinguished family and belonged to the equestrian order.
He was called Stilo (Latin stylus, "pen"), because he wrote speeches for others, and Praeconinus from his father's profession (praeco, "announcer, public crier, herald"). His aristocratic sympathies were so strong that he voluntarily accompanied Caecilius Metellus Numidicus into exile. At Rome he divided his time between teaching (although not as a professional schoolmaster) and literary work.
His most famous pupils were Varro and Cicero, and amongst his friends were Coelius Antipater, the historian, and Lucilius, the satirist, who dedicated their works to him. According to Cicero, who expresses a poor opinion of his powers as an orator, Stilo was a follower of the Stoic school. Only a few fragments of his works remain. He wrote commentaries on the hymns of the Salii (Carmen Saliare), and probably also on the Twelve Tables. He analyzed the authenticity of comedies supposedly by Plautus, and recognized 25 as canonical, four more than were allowed by Varro.
It is probable that he was the author of a general glossographical work, dealing with literary, historical and antiquarian questions. The rhetorical treatise Ad Herennium has been attributed to him by some modern scholars.