Glen Fruin (Scottish Gaelic: Gleann Freòin) is a glen in Scotland, adjacent to Loch Lomond. It contains the Fruin Water which flows into the loch, and a road, now the A817 road, known as the Glen Fruin Haul Road, which goes from the A82 up the glen and over the top of the hills to HMNB Clyde at Garelochhead.
The road from Glen Fruin to Loch Long was known as Scottish Gaelic: Rathad Mòr nan Gàidheal, (in English "The High Road of the Gaels/Highlanders").