Thailand: A Short History by David K. Wyatt is the standard one-volume history — clear, scholarly, and genuinely readable. It covers the rise of the Thai kingdoms from Sukhothai through Ayutthaya and the modernising Chakri dynasty to the late twentieth century. If you want to understand why the country looks and feels the way it does, start here.
The Railway Man by Eric Lomax is the memoir of a British officer who survived the construction of the Burma-Thailand Railway as a prisoner of war under the Japanese. Brutal and ultimately remarkable — about survival, memory, and an extraordinary act of reconciliation with a former captor. Essential reading before visiting Kanchanaburi.
Very Thai by Philip Cornwel-Smith is a witty, illustrated guide to the textures of everyday Thai life — spirit houses, noodle shops, pink taxis, the culture of sanuk. Not a narrative but endlessly useful for understanding what you're looking at.
Bangkok 8 by John Burdett is a crime novel set in the Thai capital, narrated by a Buddhist detective. It's over-the-top in places but captures the city's chaos, contradictions, and noir atmosphere better than most straightforward guides.
The Beach by Alex Garland launched a thousand backpacker fantasies — and arguably ruined a few Thai islands in the process. Worth reading for context: it tells you a great deal about the traveller mythology that still clings to the southern islands.
Anna and the King of Siam by Margaret Landon, the fictionalised account of Welsh schoolteacher Anna Leonowens at the Siamese court in the 1860s, takes considerable liberties with history. Read alongside Wyatt to keep perspective.