Shampoos and hair conditioners function primarily at or near the fiber surface. The primary function of shampoos is to remove soils or dirt from the hair surface, however, hair soils are highly varied from oily to particulate and the mechanisms for removal of these different soils also differ. Secondary functions of shampoos are also varied from conditioning the hair to dandruff control. With increasing damage to hair whether by chemical or photochemical reactions or even by abrasion, the hair surface becomes more hydrophilic and more acidic or anionic in character thus changing the affinity for different ingredients. Shampoos are often perceived as products that do not damage the hair; however damage can occur from some shampoos and such damage is described in detail. Different types of tests from laboratory to half head to tests on consumers are employed to evaluate the functionality of shampoos. These tests are described in detail with contrasts and some useful conclusions and insights. The sorption of shampoo and conditioning ingredients to hair including theories of sorption and diffusion are described in detail. Dandruff including scalp flaking, and skin irritation by surfactants is described in the last part of this chapter.