Isaac ( /ˈaɪzək/;Hebrew: יִצְחָק, Modern Yitsẖak Tiberian Yiṣḥāq, ISO 259-3 Yiçḥaq, "he will laugh"; Yiddish: יצחק, Yitskhok; Ancient Greek: Ἰσαάκ, Isaak; Latin: Isaac; Arabic: إسحاق‎ or Arabic: إسحٰق‎ʼIsḥāq) as described in the Hebrew Bible, was the only son Abraham had with his wife Sarah, and was the father of Jacob and Esau. Isaac was one of the three patriarchs of the Israelites. According to the Book of Genesis, Abraham was 100 years old when Isaac was born, and Sarah was beyond childbearing years.

Isaac was the only biblical patriarch whose name was not changed, and the only one who did not leave Canaan. Compared to those of Abraham and Jacob, Isaac's story relates fewer incidents of his life. He died when he was 180 years old, making him the longest-lived patriarch.

The anglicized name Isaac is a transliteration of the Hebrew term Yiṣḥāq which literally means "He laughs/will laugh."Ugaritic texts dating from the 13th century BCE refer to the benevolent smile of the Canaanite deity El. Genesis, however, ascribes the laughter to Isaac's parents, Abraham and Sarah, rather than El. According to the biblical narrative, Abraham fell on his face and laughed when Elohim imparted the news of their son's eventual birth. He laughed because Sarah was past the age of childbearing; both she and Abraham were advanced in age. Later, when Sarah overheard three messengers of the Lord renew the promise, she laughed inwardly for the same reason. Sarah denied laughing when Elohim questioned Abraham about it.

Isaac Erter (Yitzhak Erter; 1792–1851) was a Polish-Jewish satirist.

He was born at Janischok, Galicia. The first part of his life was full of struggles and hardships. After having associated for many years with the Hasidim, he settled at Lemberg; and through the efforts of some of his friends, such as Rapoport, Krochmal, and others, he obtained pupils whom he instructed in Hebrew language and other subjects. This comparatively happy state lasted for only three years (1813-16). Jacob Orenstein, chief rabbi of Lemberg, having been apprised of the existence among his flock of a small band occupied with the study of secular subjects, excommunicated them all. Deprived thus of his pupils, the only means of his subsistence, he settled in the neighboring town of Brody. There he struggled for a while, until he resolved to study medicine.

Erter entered (1825) the University of Budapest, where he studied medicine for five years and passed all the prescribed examinations; he then practised his new profession in various Galician towns, including Brody, where he made himself especially popular among the poor and needy, who found in him a kindly benefactor. He died at Brody.