Waterproofing is the process of making an object or structure waterproof or water-resistant so that it remains relatively unaffected by water or resisting the ingress of water under specified conditions. Such items may be used in wet environments or underwater to specified depths.

Water-resistant and waterproof often refer to penetration of water in its liquid state and possibly under pressure, whereas damp proof refers to resistance to humidity or dampness. Premeation of water vapour through a material or structure is reported as a moisture vapor transmission rate (MVTR).

Waterproofing is used in reference to building structures such as roof, swimming pool, water tank, basements, decks, or wet areas.