Biopharmaceuticals, originating from living organisms, have reshaped modern medicine by offering novel treatments for once-intractable diseases. Forecasts indicate a robust growth trajectory for the biopharmaceutical market, fueled further by imminent patent expirations stimulating the biosimilars market. Encompassing a diverse range of therapeutic products—from peptides to nucleic acid-based drugs—biopharmaceuticals are distinguished by their complexity and unique attributes, setting them apart from conventional synthetic drugs. Understanding their fundamental definitions and characteristics is essential for navigating through modern medicine and pharmacy. Notably, protein drugs, including recombinant proteins and monoclonal antibodies, dominate the landscape of approved biopharmaceuticals. However, their development is not devoid of challenges, including intricate production processes, potential immunogenicity, and regulatory compliance. Additionally, their inherent chemical instability and rapid metabolism often lead to challenged pharmacokinetics. To address these challenges, genetic engineering, glycosylation, pegylation, and other strategies emerge to enhance the efficacy, safety, and pharmacokinetic profiles of protein drugs. This chapter explores the multifaceted realm of biopharmaceuticals, with a spotlight on protein drugs, their definitions, characteristics, challenges, and boundless opportunities. The discussion underscores the critical role of genetic engineering, glycosylation, and other recent advances in augmenting the therapeutic potential of protein drugs, thereby advancing the frontiers of modern medicine.