The Dutch Water Line (Dutch: Hollandsche Waterlinie) was a series of water based defences conceived by Maurice of Nassau in the early 17th century, and realised by his half brother Frederick Henry. Combined with natural bodies of water, it could be used to transform the economic heartland of the Dutch Republic almost into an island.

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The Nieuwe Hollandse Waterlinie (New Dutch Waterline) was a military line of defence. The line was established as a protective ring approximately 85 km long and 3–5 km wide around the Dutch cities of Muiden, Utrecht, Vreeswijk and Gorinchem. It was the main Dutch defence line from 1815 till 1940.