Synthetic polymers have emerged as crucial materials for drug, gene, and vaccine delivery, offering versatile platforms for enhancing therapeutic efficacy and safety. This review provides a comprehensive overview of various synthetic polymers, including polyesters, polycarbonates, polyanhydrides, polypeptides, and polyethers, emphasizing their preparation methods and functional properties. We discuss the application of these polymers for the controlled delivery of small molecules, peptides, and proteins, highlighting their therapeutic benefits and action mechanisms. Furthermore, we explore the advances in gene delivery technologies, including plasmid DNA, oligonucleotides, and mRNA-based approaches. The review also addresses the role of synthetic polymers in vaccine delivery, focusing on protein and mRNA vaccines. By synthesizing current knowledge, we aim to outline the significant contributions of synthetic polymers to modern therapeutics and identify future directions for research in the biomedical fields.