Abscisic acid (ABA) is one of the most studied apocarotenoids in plants. Since its discovery in the early 1960s, several studies have shown that ABA regulates numerous biological processes in plants related to growth, development, and adaptive responses to environmental stresses. ABA continues to receive considerable attention in the scientific community as an important growth regulator and has recently been considered with the potential for medical use in humans. This chapter covers an overview of ABA metabolism, its chemistry, its signal transduction, and its role in drought stress and UV radiation in plants, as well as a current understanding of the application of ABA to improve tolerance, production and yield and organoleptic characteristics of economically important crops under drought stress and UV-B radiation. Similarly, we address recent findings of ABA functions in human health, and its potential use as a candidate for therapeutic use against diseases such as diabetes and cancer.