The father of corneobiology, Albert Kligman [1], wrote in 1979: ‘‘No one dies of old skin! No matter how decrepit the integument becomes after a lifetime of assaults, it continues to perform its primary protective role. . . . But skin problems abound in the aged!’’ It is now known that dry itchy senile xerotic skin is a problem of faulty epidermal and stratum corneum (SC) maturation together with desquamation. The understanding of the changes in the chemistry and function of important stratum corneum (SC) components in aging and dry skin is a result of the tenacity of a plethora of academic and industrial scientists spanning several decades. These include studies on corneocyte size [2–4]; SC lipid levels, especially ceramides [5–9]; lipid ultrastructure and biophysics [10–12]; natural moisturizing factors (NMF) [13, 14]; SC proteases [15, 16]; corneodesmosomal proteins [11, 17, 18]; and finally corneocyte quality [19, 20]. Ultimately, changes in SC cohesion and desquamatory properties were studied by Ronald Marks [21]. Some of these changes, of course, were predicted in 1964 [22]. Key in SC function and maturation, however, is its hydration [23]. It was not until 1994 that the understanding of the perturbation of water gradients in the SC of subjects with xerotic skin was developed [24] and only in 1995 [25] it was shown that water itself was essential for corneodesmosomal degradation and ultimately desquamation. This chapter gives an overview of the latest understanding of the stratum corneum and aging (> Fig. 7.1).