This book is focused on the problem of Multi Drug Resistance (MDR) and the development of MDR modulators. MDR is a major hurdle in the successful chemotherapy of various diseases. MDR is the resistance developed in the cells/ microbes towards the various structurally and functionally diverse chemotherapeutic agents. In order to tackle multi drug resistance, a variety of MDR modulators are prescribed in combination with various drugs. With the use of MDR modulators an optimum concentration of the chemotherapeutic agent could be maintained inside the infected cells.