Guanacaste is located in the northwestern part of the country, along the coast of the Pacific Ocean. To the north it borders Nicaragua. To the east is the Alajuela Province, and to the southeast is the Puntarenas Province. Guanacaste's capital is Liberia. The province covers an area of 10,141 km², and, as of 2000, had a population of 264,238. It is the most sparsely populated of all the provinces of Costa Rica.

Guanacaste's climate and culture are unique among Costa Rican provinces. The province experiences little rain and consistent heat from November to April. Tourists seek out this dry heat during the North American winter to enjoy the breathtaking Guanacastecan beaches. From May to October, the climate is similar to that of San José, consisting of showers daily and moderate temperatures. Guanacaste is, however, considerably warmer than provinces residing in higher elevations.