Surfactants, also known as wetting agents, lower the surface tension of a liquid, allowing easier spreading. The term surfactant is a compression of "Surface active agent". Surfactants are usually organic compounds that contain both hydrophobic and hydrophilic groups, and are thus semi-soluble in both organic and aqueous solvents. Surfactants are also known as amphipathic compounds, meaning that they would prefer to be in neither phase (water or organic). For this reason they locate at the phase boundary between the organic and water phase, or, if there is no more room there, they will congregate together and form micelles. The concentration at which surfactants begin to form micelles is known as the critical micelle concentration or CMC.

In Index Medicus and the National Library of Medicine (NLM, USA Dept. of Health and Human Services), "surfactant" is reserved for the meaning pulmonary surfactant (see "alveoli" link below). For the more general meaning, "surface active agent" is the heading.

Surfactants are active in:

• detergents
• emulsifiers
• paints
• adhesives
• inks
• alveoli
• wetting agents
• foamers
• defoamers
• some herbicides

List of surfactants (incomplete):

• polyethoxylated tallow amine (POEA)