Efflux mediated multidrug resistance (MDR) is a major problem in the treatment of bacterial, fungal and protozoal infections in addition to cancer chemotherapy. Among other well known mechanisms, efflux pumps are significant contributors to chemo-resistance. Efflux mediated resistance generally occurs through up-regulation of genes responsible for the expression of transporter proteins extruding drugs from the cell to create intracellular sub-therapeutic concentrations leading to resistance. The rapid expansion of MDR pathogens necessitates the discovery of resistance modifying drugs, which in combination with antimicrobial or chemotherapeutic agents would tend to reinstate the action of these drugs and avert the emergence of acquired resistance. This review describes the existence of efflux pumps in prokaryotes and eukaryotes as well as their role in chemo-resistance with a special focus on natural product-derived efflux pump inhibitors.