The temperature at which a substance boils, or changes from a liquid to a vapor or gas, through the formation and rise to the surface of bubbles of vapor within the liquid. In a stricter sense, the boiling point of a liquid is the temperature at which its vapor pressure is equal to the local atmospheric pressure.

Decreasing (or increasing) the pressure of the surrounding gases thus lowers (or raises) the boiling point of a liquid. The quantity of heat necessary to change 1 g of any substance from liquid to gas at its boiling point is known as its latent heat of vaporization.