The Ticos: Culture and Social Change in Costa Rica by Mavis Biesanz, Richard Biesanz, and Karen Biesanz — The most thorough sociological portrait of Costa Rican society, covering history, politics, family life, and national identity. Densely informative and readable.
A Guide to the Birds of Costa Rica by F. Gary Stiles and Alexander Skutch — The definitive field guide for birders, with over 850 species described. Heavy to carry but indispensable if birds are a priority.
Costa Rica: Adventures in Nature by Ree Strange Sheck — A practical guide to the national parks and nature reserves, with detailed information on trails, wildlife, and logistics.
The Earth Dwellers: Adventures in the Land of Ants by Erich Hoyt — Set partly in Costa Rica, this is an engaging popular-science account of life in a tropical ant colony. More narrative than field guide.
Costa Rica in Focus: A Guide to the People, Politics and Culture by Tjabel Daling — A concise political and cultural overview, useful background before or during a trip.
Walking with Wolf by Kay Chornook and Wolf Guindon — The story of Wolf Guindon, one of the Quaker settlers who helped establish the Monteverde Cloud Forest Reserve. A warm, firsthand account of conservation history in the region.