William or Bill Buchanan may refer to:

• William Buchanan (Manitoba politician) (1865–?), Irish-born Canadian Conservative politician
• William Buchanan (locomotive designer) (1830–1910), designed trains for the New York Central
• William Buchanan (pastoralist) (1824–1911), Australian pastoralist and gold prospector
• William Buchanan (footballer) (1911–?), Scottish amateur footballer
• William Buchanan (art dealer) (1777–1864), British art dealer
• William Izett Buchanan (born 1972), American expatriate basketball player
• William I. Buchanan (1853–1909), American diplomat
• William Ashbury Buchanan (1876–1954), journalist, publisher and politician based in Alberta
• William Murdoch Buchanan (1897–1966), Canadian politician and dentist
• Bill Buchanan (24), a fictional character in 24
• Bill Buchanan (computer scientist) (born 1961), Scottish computer scientist
• Bill Buchanan (songwriter) (1930–1996), American songwriter
• Billy Buchanan (1924–1999), Scottish footballer with Carlisle United and Barrow