Dew is water in the form of droplets that appears on thin, exposed objects in the morning or evening. As the exposed surface cools by radiating its heat, atmospheric moisture condenses at a rate greater than that at which it can evaporate, resulting in the formation of water droplets.

When temperatures are low enough, dew takes the form of ice; this form is called freeze (frost is, however, not frozen dew).

Because dew is related to the temperature of surfaces, in late summer it is formed most easily on surfaces which are not warmed by conducted heat from deep ground, such as grass, leaves, railings, car roofs, and bridges.

Dew should not be confused with guttation, which is the process by which plants release excess water from the tips of their leaves.