The Forth rises in Loch Ard in the Trossachs, a mountain range some 30 km (19 miles) west of Stirling. It flows roughly eastward, through Aberfoyle, joining with the Duchray Water and Kelty Water, and out over the flat expanse of the Flanders Moss. It is then joined by the River Teith (which itself drains Loch Venachar, Loch Lubnaig, Loch Katrine, and Loch Voil) and the River Allan, before meandering through the ancient city of Stirling. At Stirling the river widens and becomes tidal, and it is here that the last (seasonal) ford of the river exists. From Stirling, the Forth flows east over the Carse of Stirling and past the towns of Cambus (where it is joined by the river Devon), Alloa and Airth. Upon reaching Kincardine the river begins to widen into an estuary, the Firth of Forth.
There are a number of towns which line the shores, as well as the petrochemical complexes at Grangemouth, the commercial docks at Leith, oilrig construction yards at Methil, the ship-breaking facility at Inverkeithing and the naval dockyard at Rosyth, with numerous other industrial areas including the Forth Bridgehead area, Burntisland, Kirkcaldy, Bo'ness and Leven.
Upstream of Stirling, the river is rather small and is crossed in numerous places (although prior to modern drainage works, the ground was often treacherously marshy near the riverbank). After its confluence with the Teith and Allan, the river is sufficiently wide that a significant bridge is required. A bridge has existed at Stirling since at least the 13th century, and until the opening of the road crossing at Kincardine in 1936, Stirling remained the easternmost road crossing. Much further downstream at Queensferry the famous rail bridge opened in 1890 and a modern road bridge in 1964. A swinging railway bridge between Alloa on the north shore and Throsk on the south opened in 1885 and was closed (and largely demolished) in 1970.
Plans to construct a new road bridge slightly to the West of the existing Forth road Bridge have been announced by the Scottish Executive. It is planned to open in 2016.