This review provides an overview of the role of polymers in drug delivery systems, highlighting their fundamental principles and recent advancements. Polymers have played a crucial role in advancing drug delivery technology by enabling controlled release of therapeutic agents over extended periods, cyclic dosing, and tunable release of both hydrophilic and hydrophobic drugs. The field has evolved significantly, driven by innovations in chemical engineering, with modern drug delivery systems now tailored for specific cargo and engineered to exert distinct biological functions. The review covers conventional applications of polymers in drug delivery, including diffusion-controlled, solvent-activated, and biodegradable systems. It discusses the mathematical foundations of drug delivery systems and the physiological barriers to drug delivery. The origins and applications of stimuli-responsive polymer systems, such as temperature- and pH-responsive polymers, are explored, along with polymer therapeutics like polymer-protein and polymer-drug conjugates. Recent developments in polymers capable of molecular recognition or directing intracellular delivery are surveyed, emphasizing areas of research that advance the frontiers of drug delivery. The review also delves into the pharmacological considerations in drug delivery, including oral and parenteral delivery mechanisms, and the physiological pH variations in different body compartments. The section on responsive systems based on temperature and pH highlights the use of these stimuli to modulate polymer behavior, while the section on redox-responsive polymers discusses the potential of polymers containing labile linkages for biodegradable or bioerodible delivery devices. The review concludes with a discussion on polymer therapeutics, including polymer-drug and polymer-protein conjugates, and their applications in targeted drug delivery and combination therapies.This review provides an overview of the role of polymers in drug delivery systems, highlighting their fundamental principles and recent advancements. Polymers have played a crucial role in advancing drug delivery technology by enabling controlled release of therapeutic agents over extended periods, cyclic dosing, and tunable release of both hydrophilic and hydrophobic drugs. The field has evolved significantly, driven by innovations in chemical engineering, with modern drug delivery systems now tailored for specific cargo and engineered to exert distinct biological functions. The review covers conventional applications of polymers in drug delivery, including diffusion-controlled, solvent-activated, and biodegradable systems. It discusses the mathematical foundations of drug delivery systems and the physiological barriers to drug delivery. The origins and applications of stimuli-responsive polymer systems, such as temperature- and pH-responsive polymers, are explored, along with polymer therapeutics like polymer-protein and polymer-drug conjugates. Recent developments in polymers capable of molecular recognition or directing intracellular delivery are surveyed, emphasizing areas of research that advance the frontiers of drug delivery. The review also delves into the pharmacological considerations in drug delivery, including oral and parenteral delivery mechanisms, and the physiological pH variations in different body compartments. The section on responsive systems based on temperature and pH highlights the use of these stimuli to modulate polymer behavior, while the section on redox-responsive polymers discusses the potential of polymers containing labile linkages for biodegradable or bioerodible delivery devices. The review concludes with a discussion on polymer therapeutics, including polymer-drug and polymer-protein conjugates, and their applications in targeted drug delivery and combination therapies.