凝华是指一种物质从气态不经过液态直接转化为固态的过程，是物质在温度和气压高于三相点的时候发生的物态变化。

凝华是放热反应。常见的例子有结霜。

与凝华相反的过程称做升华，指物质从固态直接变成气态。

Deposition is a thermodynamic process, a phase transition in which gas transforms into solid. The reverse of deposition is sublimation.

One example of deposition is the process by which, in sub-freezing air, water vapor changes directly to ice without first becoming a liquid. This is how snow forms in clouds, as well as how frost and hoar frost form on the ground or other surfaces. Another example is when frost forms on a leaf. For deposition to occur, thermal energy must be removed from a gas. When the leaf becomes cold enough, water vapor in the air surrounding the leaf loses enough thermal energy to change into a solid. Even though the air temperature may be below the dew point, the water vapor may not be able to condense spontaneously if there is no way to remove the latent heat. When the leaf is introduced, the supercooled water vapor immediately begins to condense, but by this point is already past the freezing point. This causes the water vapor to change directly into a solid.