A drainage divide, water divide, divide or in North America watershed is the line that separates neighbouring drainage basins (catchments). In hilly country, the divide lies along topographical peaks and ridges, and may be in the form of a single range of hills or mountains (known as a Dividing range). In flat country—especially where the ground is marshy—the divide may an invisible, more or less notional line on the ground on either side of which falling raindrops journey to different rivers, and even to different sides of a region or continent.

Drainage divides are important geographical, and often also political boundaries. Roads (such as ridgeways) and rail tracks often follow divides to minimise grades (gradients), and to avoid marshes and rivers.^{[citation needed]}

A divide is known by other names:

Drainage divides can be grouped in three types:

Drainage divides hinder river navigation. In pre-industrial times, water divides were crossed at portages. Later, canals connected adjoining drainage basins.