The evolution in the synthesis of smart polymers broadens new horizons for their potent application in medicine, especially in drug delivery. Many synthetic polymers that exhibit environmentally responsive behavior are potential smart carrier candidates that allow for controlled therapeutic delivery. These materials can be loaded with specifi c drugs for therapeutic applications, releasing treatment in response to a stimulus. This stimuli-responsive capability has enabled smart polymeric materials to distribute drugs in response to commonly known exogenous and/ or endogenous stimuli. Examples of these various stimuli include pH, enzyme concentration, temperature, ultrasound intensity, as well as light, magnetic fi eld, redox gradients and a multitude of other potential stimuli. This chapter provides a detailed critical discussion and an overview of the stimuli-responsive polymers which have found applications in targeted drug delivery. Furthermore, multiresponsive systems and their forthcoming development as well as challenges associated with some stimuli-responsive systems are discussed. Finally, the most recent and emerging trends along with a look toward expected future breakthroughs using these types of nanocarriers are discussed.