The limestone region of PR covers about 27% of the island1s surface and has karst features. The karst belt (KB), that part of the northern limestone with the most spectacular karst landforms, covering 65% of the northern limestone, is the focus here. Chapters: geography; features: geomorphological, hydrological, and ecological diversity; nat1l. resources; econ. importance: water, other minerals, ag., forestry, and environ. disturbances; history of intensive use; vulnerable to human activity: cutting vs. paved over forests, draining vs. filling wetlands, conversion vs. trans1n. of land uses, pumping vs. overdrafting aquifers, contaminating vs. poisoning ground water, and surface water pollution; and proposal for transferring KB to the public domain. Color photos.