Recent medical advances are closely tied to real-time healthcare monitoring, revolutionizing precise diagnosis, personalized treatments, and effective disease prevention. By continuously tracking the body’s internal processes—such as bio-signals, biochemical parameters, and biomarkers in biofluids—biosensors generate vital health information that enhances patient care. These sensors, available in wearable, implantable, and ingestible forms, measure specific chemical or biological reactions, producing real-time signals that reflect the concentration of targeted analytes. Beyond biochemical monitoring, physical sensors are crucial in tracking physiological metrics such as body temperature, heart rate, pressure, and movement. Integrating biochemical and physical monitoring offers a comprehensive health-tracking system, improving diagnostic accuracy and optimizing treatment efficacy. In recent years, significant investments from scientific and commercial sectors have driven the development of body-integrated technologies. However, key challenges remain in optimizing sensor design, selecting suitable materials, and ensuring biocompatibility and biodegradability. This chapter presents an in-depth exploration of the current state of sensor technology, highlighting the technical challenges and their transformative impact on modern medicine.