Red Clydeside was the era of political radicalism in Glasgow, Scotland, and areas around the city, on the banks of the River Clyde, such as Clydebank, Greenock, Dumbarton and Paisley, from the 1910s until the early 1930s. Red Clydeside is a significant part of the history of the labour movement in Britain as a whole, and Scotland in particular.

John Maclean was a Scottish schoolteacher and revolutionary socialist of the Red Clydeside era. He was notable for his outspoken opposition to World War I, which caused his arrest under the Defence of the Realm Act and loss of his teaching post, after which he became a full-time Marxist lecturer and organiser. In April 1918 he was arrested for sedition, and his 75-minute speech from the dock became a celebrated text for Scottish left-wingers. He was sentenced to five years' penal servitude, but was released after the November armistice.