**1. Introduction**

Licorice (liquorice), the underground portion of *Glycyrrhiza* species, has been used as a remedy for various types of stress, inflammatory diseases, digestive organ disorders, and pain in traditional medicine in Asian and European countries [1, 2]. The main constituent, glycyrrhizin, and the associated aglycone, glycyrrhetinic acid, are also used in modern medicine, whereas the phenolic constituents have been implicated in promoting improved health, particularly with regard to stomach ulcers [2]. Therefore, several research groups have investigated the phenolic constituents of licorice [3] and found that it has beneficial effects for health, including antimicrobial properties [4, 5]. In this chapter, we summarize our studies on phenolic constituents and some of their pharmacological effects, including those linked to drug-resistant bacteria.
