Immunological detection methods play an important role in identifying specific biomarkers for disease diagnosis, prognosis, and treatment in precision medicine. With the recent attention shifted towards personalized treatments, immunological detection methods provide a platform for acquiring precise and accurate information using immunoassays. These assays operate on the principle of antigen–antibody interaction to identify disease-specific biomarkers in clinical application. In immunoassays, the antibody–antigen complex is detected through end-reaction outputs that can be analyzed both qualitatively and quantitatively. This book chapter discusses common immunoassays employed in clinical and research settings, emphasizing specificity and accuracy of each method. The chapter will also highlight some recent advancements in immunoassay technology.