This chapter focuses on the biomedical role of biosensors, tracing their evolution from diagnostic tools to intelligent health-monitoring systems. Section 3.1 outlines key clinical applications, including disease detection, cancer biomarker monitoring, therapeutic drug tracking, and wearable health technologies that enable continuous patient observation. Section 3.2 discusses emerging directions, miniaturization, smartphone-linked devices, nanomaterial-enhanced sensitivity, and AI-driven data analysis, while addressing challenges of biocompatibility, long-term performance, and ethics. Together, these sections present biosensors as integral components of modern medicine, transforming biological signals into actionable medical insight.