According to Genesis, Noah took seven pairs of clean animals onto the Ark.
Genesis 7:2–3 distinguishes clean animals from animals that were not clean. It instructs Noah to take seven pairs of the clean animals, male and female, and one pair of the animals that were not clean. The passage also gives seven pairs of birds, described as male and female, so their offspring could continue on the earth.
This detail is often remembered incorrectly as one pair of every animal. That simpler version does not match Genesis 7:2–3, which makes a distinction between categories. Genesis 6:19–20 gives an earlier general instruction to bring pairs of every kind, while the later passage adds the more specific numbers.
The text does not provide a modern zoological definition of “clean.” In the biblical context, the classification relates to ritual and sacrificial concerns; after leaving the Ark, Noah offers some clean animals in sacrifice in Genesis 8:20.