Puerto Rico's high population density (430/km 2 ) and concentrated development in the coastal zone result in communities that are highly to extremely vulnerable to coastal hazards. Tsunamis pose the greatest extreme risk (e.g., 1867 southeast coast; 1918 northwest coast), and westward-moving hurricanes have a history of severe impact (e.g., Hurricane Hugo, 1989; San Ciriaco Hurricane, 1899). The north and west coasts experience far-traveled swell from North Atlantic winter storms (e.g., the Perfect Storm of 1991) which severely impact the coast. Sea-level rise threatens flooding of low-lying coastal mangroves, wetlands, and low-elevation developments, and erosion of wave-cut bluffs will accelerate (e.g., south coast Municipios [equivalent of counties] of Arroyo and Guayama, just west of Cabo Mala Pascua). Anthropogenic effects have seriously modified coastal processes to create high- to extreme-risk zones. Examples include removal of protective dunes and beach sediment by sand mining (e.g., Piñones, Caribe Playa Seabeach Resort, and Camuy), and erosional impacts due to marinas (e.g., erosion rates of 3 m/yr in Rincón area due to Punta Ensenada marina). Communities have taken poor courses in erosion control by emplacing shore-hardening structures along over 50 separate coastal stretches (e.g., seawalls at San Juan Harbor and Arecibo; groins in Ensenada de Boca Vieja), and utilizing poor construction designs (e.g., gabions). Beach profiling reveals that beaches narrow and disappear in front of such structures (no dry beach in front of 55% of seawalls surveyed). Mitigation must come through prohibiting construction in high-risk zones, encouraging wider adoption of setback principles (e.g., Villa Palmira), relocating after storms, enforcing anti–sand-mining regulations, and better public education.