Crawlspace moisture is one of the most pervasive and damaging conditions found during home inspections. A damp crawlspace can create an environment that promotes wood decay, structural damage, mold growth, pest infestations, and degraded indoor air quality in the home. Because of the stack effect, a meaningful share of the air in the living space can originate from the crawlspace, meaning moisture, mold spores, and contaminants there may affect the air occupants breathe. Despite being out of sight and often out of mind, the crawlspace plays a critical role in a home's structural integrity, energy efficiency, and healthfulness. Moisture enters crawlspaces from multiple sources including groundwater, surface water drainage, plumbing leaks, and water vapor migrating through the soil. Without proper moisture management, these sources create persistently damp conditions that accelerate deterioration of floor framing, subfloor sheathing, insulation, and mechanical systems. Understanding crawlspace moisture dynamics, identifying the warning signs, and implementing effective solutions protects both the home's structure and its occupants' health. This comprehensive guide covers everything homeowners, buyers, and inspectors need to know about crawlspace moisture.