Beyond the Mexique Bay by Aldous Huxley (1934). Huxley travelled through Central America and the Caribbean in the early 1930s, passing through what was then British Honduras. His observations on the colonial towns, the jungle, and the people — sharp, occasionally condescending, always alive — remain unexpectedly readable. The Belize sections are brief but vivid, and the broader Central American context helps frame the region.
The Last Flight of the Scarlet Macaw by Bruce Barcott (2008). The story of Sharon Matola, the founder of the Belize Zoo, and her fight against a dam project that would have flooded a major river valley. Not set on Ambergris Caye, but essential reading for anyone who wants to understand how Belize works: the politics, the conservation battles, the tension between development and the natural environment that makes the reef worth protecting.
Time Among the Maya by Ronald Wright (1989). Wright travelled through the Maya world from Belize to Mexico, spending time with communities that still carry the culture. The Belize sections cover both the archaeology and the living communities. A useful corrective to the tendency to treat Maya sites as ruins rather than as part of an ongoing civilisation.
The Coral Triangle — for the scientifically minded, any book on reef ecology will deepen a diving trip. The specifics of the Belize reef system — the species, the pressures, the UNESCO designation — make more sense after reading about how barrier reefs actually work. Elizabeth Kolbert's The Sixth Extinction covers reef bleaching and acidification with characteristic clarity, even if it is not about Belize specifically.