According to the Book of Genesis, Ishmaelites are the descendants of Ishmael, the elder son of Abraham.

According to the Book of Genesis, Abraham's first wife was named Sarah and his second wife Hagar. However Sarah was old and barren, and could not conceive. According to Genesis 16:3 Sarah (then Sarai) gave her maid Hagar in marriage to Abraham, in order that Abraham might have an heir. Genesis 16: 3 states, "And Sarai Abram's wife took Hagar her maid....and gave her to her husband Abram to be his wife”. Hagar conceived Ishmael from Abraham, and the Ishmaelites descend from him.

After Abraham pleaded with God for Ishmael to live under his blessing, Genesis 17:20 states, "But as for Ishmael, I have heard thee: behold I have blessed him, and will make him fruitful, and will multiply him exceedingly; twelve princes shall he beget, and I will make him a great nation."

Genesis goes on to record that the Ishmaelites went on to control the vast region north of Havilah stretching from Shur before Egypt northwest towards Assyria. Traditions regarding their rise to greatness are found in Midrashic works such as the Sefer Ha-Yashar which records that they had conquered the territory in a war with the sons of Tarshish.