Biomarkers are essential tools in modern healthcare, offering measurable indicators of biological processes, disease states, and therapeutic responses. This chapter explores the pivotal role of biomarkers in precision healthcare, categorizing them into molecular, biophysical, and digital types, and emphasizing their importance in enabling personalized medicine. Molecular biomarkers, such as deoxyribonucleic acid (DNA), ribonucleic acid (RNA), and protein-based markers, are central to disease detection and treatment stratification, with applications in cancer, cardiovascular diseases, and neurodegenerative disorders. Physiological biomarkers, including vital signs like heart rate, blood pressure, and oxygen saturation, are increasingly monitored in real time through wearable devices and bioelectronic sensors, transforming chronic disease management. Inflammatory and immune biomarkers, such as cytokines and C-reactive protein (CRP), provide critical insights into the immune response and inflammation, aiding in the diagnosis and management of autoimmune and infectious diseases. The integration of digital biomarkers, derived from mobile health platforms, wearables, and AI-driven algorithms, further enables continuous monitoring of mental health, lifestyle factors, and sleep patterns, offering a comprehensive view of individual health. This chapter also highlights emerging trends in biomarker-based monitoring, including advances in biosensor technologies, multi-omics integration, and the convergence of artificial intelligence and bioelectronics. It concludes by addressing the regulatory and ethical challenges inherent in biomarker-driven healthcare and envisions a future where predictive and preventive health monitoring redefines personalized care. This comprehensive overview underscores the transformative potential of biomarkers in improving health outcomes and advancing precision medicine.