This book will give an insight into the interactions of bio-surfactants (bile-salts) with conventional surfactants and drugs. Also how they are useful in solubilizing the drugs. Bile salts as potential bio-surfactants to solubilize drugs of interest are discussed giving an insight into the selection of drugs in different applications as their properties get modified by interaction with bile salts, thus influencing their solution behavior which, in turn, modify the phase-forming behvaiour, microemulsion, clouding phenomenon, besides solubilization.