Loch Ness is a large freshwater loch in the Scottish Highlands extending for approximately 37 kilometres southwest of Inverness. It takes its name from the River Ness, which flows from the northern end. Loch Ness is best known for claimed sightings of the cryptozoological Loch Ness Monster, also known affectionately as "Nessie". It is one of a series of interconnected, murky bodies of water in Scotland; its water visibility is exceptionally low due to the high peat content of the surrounding soil. The southern end connects to Loch Oich by the River Oich and a section of the Caledonian Canal. The northern end connects to Loch Dochfour via the River Ness, which then ultimately leads to the North Sea via the Moray Firth.

Loch is a word meaning "lake" or "sea inlet" in Scottish and Irish Gaelic, subsequently borrowed into English. In Irish contexts, it often appears in the anglicized form "lough".