Biomarkers are critical indicators of biological processes, disease progression, and therapeutic responses, playing a key role in precision healthcare. They enable early disease detection, monitoring, and personalized treatment strategies. Biosensors, as advanced analytical tools, allow rapid and specific biomarker detection across clinical and point-of-care settings. Their advantages, including cost-effectiveness, user-friendliness, high sensitivity, and real-time monitoring, make them invaluable in modern diagnostics and health management. This chapter introduces the fundamental concepts of biomarkers, discussing their classifications and biological significance. Additionally, we explore biosensing technologies designed for biomarker detection, focusing on their applications in disease diagnosis, prognosis, and treatment monitoring. By bridging biomarker research with biosensor advancements, this chapter provides insights into their transformative impact on precision healthcare and encourages further exploration in this evolving field.