Loch Lomond is a freshwater Scottish loch which crosses the Highland Boundary Fault, often considered the boundary between the lowlands of Central Scotland and the Highlands. Traditionally forming part of the boundary between the counties of Stirlingshire and Dunbartonshire, Loch Lomond is split between the council areas of Stirling, Argyll and Bute and West Dunbartonshire. Its southern shores are about 23 kilometres (14 mi) northwest of the centre of Glasgow, Scotland's largest city. The Loch forms part of the Loch Lomond and The Trossachs National Park which was established in 2002.

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".