This chapter delves into the necessity, evolution, and implementation of the Maximal Usage Trial (MUsT) paradigm in dermal drug development. It provides a review of the state of dermal absorption evaluation prior to the MUsT, highlighting the initial resistance to its adoption and the subsequent adoption and implementation. The chapter also offers insight into the utility of MUsT in the area of regulatory evaluation, showcasing its impact on the field of dermal drug development. Furthermore, it provides a glimpse into the emerging tools and technologies on the horizon, poised to enhance our understanding of dermal absorption evaluation. This chapter serves as a valuable resource for researchers, scientists, and industry professionals seeking to understand the MUsT paradigm and its significance in dermal drug development.