Craignethan Castle is a ruined castle in South Lanarkshire, Scotland. It is located above the River Nethan, a tributary of the River Clyde, at NS816464. The castle is two miles west of the village of Crossford, and 4.5 miles north-west of Lanark. Built in the first half of the 16th century, Craignethan is recognised as an excellent early example of a sophisticated artillery fortification, although its defences were never fully tested.

Sir James Hamilton of Finnart was a Scottish nobleman and architect, the illegitimate son of James Hamilton, 1st Earl of Arran, and Marion Boyd of Bonshaw. Although legitimated in 1512 while still a minor, he continued to be known as the "Bastard of Arran". As a key member of the Hamilton family, and second cousin of James V, King of Scotland, he became a prominent member of Scottish society.