Biosimilars have transformed treatment modalities across various medical fields such as oncology, rheumatology, and immunology. Despite their potential for reducing healthcare costs, concerns persist regarding their ability to induce an immune response, which could affect efficacy and safety. This review critically evaluates the current evidence on the immunogenicity of biosimilars and discusses the regulatory frameworks guiding their approval and monitoring. This review includes studies from databases like Scopus, PubMed, Web of Science, and ScienceDirect, published up to April 2024. It explores the 'totality of the evidence' approach used by regulatory bodies like the FDA and EMA, detailing analytical, preclinical, and clinical assessments that ensure biosimilars' similarity to their reference products in terms of structure, function, and clinical outcomes. The review also addresses the challenges and limitations in current research methodologies and the implications of immunogenicity on therapeutic efficacy and patient safety. While substantial evidence confirms the safety and efficacy of biosimilars, the review emphasizes the need for continuous regulatory vigilance and advanced methodologies in post-marketing surveillance to capture long-term immunogenicity data effectively. It advocates for integrating cutting-edge analytical techniques and personalized medicine to better manage immunogenic risks associated with biological therapies.