Infiltration may refer to:
- Infiltration (HVAC), a heating, ventilation, and air conditioning term for air leakage into buildings
- Infiltration (hydrology), downward movement of water through soil
- Infiltration/Inflow, leakage of groundwater into sanitary sewers
- Infiltration (medical), the diffusion or accumulation of substances not normal to it or in amounts in excess of the normal
- Infiltration (zine), a popular urban exploration zine/website created by Jeff Chapman (Ninjalicious)
- Infiltration tactics, tactics developed by the German army in 1917 that broke the trench-warfare stalemate on the western front
- An attempt to sneak across a border, or into a guarded place
- Entryism, a political tactic aimed at dissolving potentially harmful organizations or political adversaries
- Espionage, an attempt to infiltrate a target organization
- Urban exploration, exploring parts of towns etc. which are normally off-limits
- Infiltration, a book by Albert Speer