**1.1 Objectives**

The purpose of this chapter is to present applications of the PA technique in skin research, both in the characterization of skin itself and in transdermal drug delivery studies. The basic experimental setup for such studies will be briefly presented, aiming to help those who may be interested in developing similar studies. Emphasis will be done to *in vivo* measurements, because of its importance in this field. Our objective is to show the usefulness of the PA technique in the biomedical field, particularly in skin research; finally, perspectives for future work in this field will be presented.
