Simon I (1076 – 13 January 1138) was the duke of Lorraine from 1115 to his death, the eldest son and successor of Thierry II and Hedwige of Formbach.

Continuing the policy of friendship with the Holy Roman Emperor, he accompanied the Emperor Henry V to the Diet of Worms of 1122, where the Investiture Controversy was resolved.

He had stormy relations with the espiscopates of his realm: fighting with Stephen of Bar, bishop of Metz, and Adalberon, archbishop of Trier, both allies of the count of Bar, whose claim to Lorraine against Simon's father had been quashed by Henry V's father Henry IV. Though Adalberon excommunicated him, Pope Innocent II lifted it. He was a friend of Bernard of Clairvaux and he built many abbeys in his duchy, including that of Sturzelbronn in 1135. There was he interred after his original burial in Saint-Dié.

His wife was Adelaide (d.1158), daughter of Gerard of Supplinburg, count of Querfort, and sister of the Emperor Lothair II. With her he had:
• Matthias, his successor in Lorraine
• Robert, lord of Floranges (near Thionville)
• Agatha, married Reginald III, Count of Burgundy, the first Free Count
• Hedwige, married Frederick III, count of Toul
• Bertha, married Margrave Hermann III of Baden
• Matthias
• Baldwin
• John