The chapter discusses the role of proton-dependent multidrug efflux systems in bacterial and eukaryotic cells, highlighting their importance in conferring resistance to toxic compounds. These systems are primarily driven by the proton motive force (PMF) and can handle a wide range of structurally dissimilar compounds, posing a significant clinical threat. The best-characterized example is P-glycoprotein, which is involved in multidrug resistance in humans. However, other proton-dependent multidrug efflux systems, such as those belonging to the major facilitator superfamily (MFS), resistance/ nodulation/cell division (RND) family, and small multidrug resistance (SMR) family, are also discussed. These systems are involved in the transport of various substrates and are regulated by different mechanisms, including transcriptional control and substrate-induced expression. The chapter details the structural and functional characteristics of these systems, including the roles of specific residues and motifs in substrate recognition and transport. Additionally, it explores the potential for these systems to mediate novel mechanisms of drug resistance, such as the accumulation of toxic compounds within intracellular vesicles. The chapter concludes by discussing the structural and functional diversity of MFS proteins and the possibility that other members of this family may also mediate multidrug antiport.The chapter discusses the role of proton-dependent multidrug efflux systems in bacterial and eukaryotic cells, highlighting their importance in conferring resistance to toxic compounds. These systems are primarily driven by the proton motive force (PMF) and can handle a wide range of structurally dissimilar compounds, posing a significant clinical threat. The best-characterized example is P-glycoprotein, which is involved in multidrug resistance in humans. However, other proton-dependent multidrug efflux systems, such as those belonging to the major facilitator superfamily (MFS), resistance/ nodulation/cell division (RND) family, and small multidrug resistance (SMR) family, are also discussed. These systems are involved in the transport of various substrates and are regulated by different mechanisms, including transcriptional control and substrate-induced expression. The chapter details the structural and functional characteristics of these systems, including the roles of specific residues and motifs in substrate recognition and transport. Additionally, it explores the potential for these systems to mediate novel mechanisms of drug resistance, such as the accumulation of toxic compounds within intracellular vesicles. The chapter concludes by discussing the structural and functional diversity of MFS proteins and the possibility that other members of this family may also mediate multidrug antiport.