Many materials made from fats and oils derive their importance from their ability to modify the surface behavior of the liquid in which they are dissolved. These compounds are grouped under the broad classification of surface active agents or surfactants. Depending on their use, they are classified as detergents, wetting agents, emulsifiers, dispersing agents, etc. The oldest, and still one of the most important surfactants, is ordinary soap; twentythree percent of all the tallow produced in the United States goes into soap. This paper covers the present state of the art of soap technology, and the most important classes of fat‐based surfactants.