According to Genesis, God placed a rainbow in the clouds as the sign of the covenant after the Flood.
Genesis 9:12–17 describes the rainbow as a sign of the covenant between God and Noah, his descendants, and every living creature. The covenant promises that a flood will not again destroy all flesh, and the rainbow is presented as its visible reminder.
The passage does not say that rainbows first began to exist after the Flood. Instead, it assigns the rainbow a covenantal meaning within the story. This is why the account’s emphasis is on what the rainbow signifies rather than on its physical origin.
In modern culture, the rainbow has many additional associations, including meteorology, peace, and diverse social movements. Those later meanings should not be confused with the specific covenant symbolism in Genesis 9.