This chapter provides a foundational overview of medical devices as essential instruments in contemporary healthcare systems. It traces the historical evolution of devices, from rudimentary surgical tools to today’s AI-driven diagnostics and personalized monitoring technologies. Emphasis is placed on how devices have transitioned from hospital-centric tools to user-oriented, connected technologies that empower patients and clinicians alike. The chapter explores the broad categorization of devices, from implantables and wearables to imaging systems and digital therapeutics, highlighting their role across the continuum of care. It underscores the significance of medical devices in early diagnosis, minimally invasive treatment, and long-term disease management. Key milestones in innovation are discussed, including breakthroughs in cardiac implants, dialysis machines, and robotic surgery. These technologies are examined not only in terms of clinical value but also in light of their global reach, with examples from high-income countries and low- and middle-income settings alike. Attention is given to how different health systems adopt and adapt devices based on infrastructure, economic capacity, and policy. The chapter contrasts mature and emerging markets, exposing disparities in access and technology diffusion. It also introduces the importance of multidisciplinary collaboration in device development and lays the groundwork for later chapters that examine stakeholders, regulation, and market dynamics. Medical devices are positioned not just as products, but as integral enablers of accessible, effective, and equitable global healthcare.