Smart polymeric materials respond by large changes due to small changes in environment. The polymers that form these smart materials are referred as “smart” polymers or “stimuliresponsive” polymers or “environmentally” sensitive polymers. The smart polymers undergo fast and reversible changes in the microstructure from a hydrophilic to ahydrophobic state that are triggered by small stimuli in the environment. The changes are apparent at the macroscopic level as precipitate formation from a solution accompanied by phase separation from aqueous solution or order of magnitude changes in the hydrogel size. This whole phenomenon is reversible, the system returning to its initial state when the trigger is removed. The driving force behind these transitions varies, with common stimuli including neutralization of charged groups by either a pH shift or the addition of an oppositely charged polymer, changes in the efficiency of the hydrogen bonding with an increase in temperature or ionic strength, and collapse of hydrogels and interpenetrating polymer networks. Even the latest among these have been the electric, magnetic, light or radiation induced reversible phase transitions. Such property change of smart polymers has shown various applications in biological systems.