Isaac Bernays (/bɜːrˈneɪz/ bur-NAYZ, German: [bɛʁˈnaɪs], Yiddish: יצחק איצק בערנייז, romanized: Yitsḥak Itsik Bernayz; 29 September 1792 – 1 May 1849) was Chief Rabbi in Hamburg.

He was the son of Jacob Gera, a boarding house keeper at Mainz, and an elder brother of Adolphus Bernays.

In 1821 he was elected chief rabbi of the German-Jewish community in Hamburg, to fill a position where a man of strictly Orthodox views but of modern education was wanted as head of the congregation.

He added lessons in German, natural science, geography, and history as important parts of the curriculum, and by 1827 what had formerly been merely a religious class had been changed to a good elementary public school.

Bernays possessed wide philosophical views, a rare knowledge of the Bible, Midrash, and Talmud, and an admirable flow of language: he was indeed a born orator.

By lectures on the Psalms, on Judah ha-Levi's Kuzari etc., he tried to strengthen and to deepen the religious life of the community, the institutions of which he supervised very carefully.

One of his sons, Louis Bernays is mentioned in the annals of the Jewish Community of Baden, Switzerland, as one of its ten founders in the year 1859.