The integration of wearable sensors into healthcare has revolutionized health monitoring by enabling real-time, continuous tracking of physiological, biochemical, and behavioral parameters. This chapter explores the advances and challenges in wearable sensor technologies, focusing on their role in precision healthcare. It begins by discussing the evolution of wearables from single-sensor devices to sophisticated multimodal systems capable of capturing comprehensive health data. This chapter delves into key technological advancements, such as flexible materials, nanobiosensors, microfluidics, and artificial intelligence (AI)-driven analytics, which have enhanced the accuracy, reliability, and usability of wearable sensors. This chapter also examines the applications of wearable sensors in personalized medicine, emphasizing their potential to tailor treatments and preventive strategies to individual health profiles. It underscores the importance of hybrid systems that integrate physiological and biochemical sensors, enabling a holistic understanding of complex health conditions. Challenges such as data accuracy, privacy, and regulatory compliance are critically addressed, with strategies like sensor fusion, advanced calibration methods, and robust data security measures highlighted as solutions. Future directions are explored in this chapter, including next-generation sensors, the integration of wearables with AI and big data, and their impact on global health and preventive medicine. Ethical and societal implications, such as data ownership and health equity, are also considered. This chapter concludes by underscoring the transformative potential of wearable sensors to advance personalized, data-driven healthcare while addressing critical challenges to their widespread adoption.