Leopold III (1073 – November 15, 1136), Margrave of Austria 1095-1136, also known as Saint Leopold (his feast day being November 15), patron saint of Austria in general and of Vienna, Lower Austria and jointly with Saint Florian of Upper Austria in particular.

Leopold was the son of Margrave Leopold II and Ida of Formbach-Ratelnberg; his sons were Leopold IV and Henry II Jasomirgott. His second wife was Agnes, the sister of Emperor Henry V, since he had supported the latter against his father Henry IV. This connection to the Salians raised the importance of the House of Babenberg, to which important royal rights on the territory of its margraviate were granted. Leopold called himself "Princeps Terrae", which rose from a consciousness of independent territorial rule. He was considered as a candidate for the election of the King of Germany in 1125, but declined this opportunity.

He is mainly remembered for the development of the country, which is associated with him founding monasteries. His most important foundation is Klosterneuburg (1108). According to legend, the Lady Mary appeared to him and led him to a position where he found the veil of his wife Agnes, lost years before. At that place, the monastery of Klosterneuburg was founded. He subsequently expanded this city to become his residence.

Other foundations were Heiligenkreuz, Kleinmariazell and Seitenstetten. All of those induced the church to canonize him in 1485. In fact, the monasteries served the purpose of developing a territory still largely covered by forest at that time.

Leopold also fostered the development of cities, namely besides Klosterneuburg and Vienna also Krems, which was endowed with a mint, which, however, never attained great importance.
The first literary texts from the area of Austria date back to Leopold's time, which are the writings of Henry of Melk and Ava of Göttweig.

He is buried in the Klosterneuburg monastery, which owes him its existence. In 1663, under the rule of his namesake Emperor Leopold I, he was declared patron saint of Austria instead of Saint Koloman. His feast day, November 15, is a school holiday in Vienna, Lower Austria and Upper Austria.