Chapter 1 of the Digital Medicine Starter Guide lays the foundational framework for understanding what Digital Medicine truly is—and what it is not. In an era where terms like “digital health,” “wellness tech,” and “health IT” are often used interchangeably, this chapter provides a clear, clinically grounded delineation of Digital Medicine as a distinct and rigorously validated subset of the broader digital health landscape. The chapter opens by framing Digital Medicine as a transformative force in healthcare: no longer a futuristic vision, but an integrated reality redefining how we diagnose, treat, and manage health conditions. It highlights how telemedicine, AI-driven decision support, wearable biosensors, and digital therapeutics (DTx) revolutionize care delivery by enabling precision, personalization, and proactive intervention. The chapter defines the core characteristics of Digital Medicine through a structured approach, emphasizing scientific validation, integration into clinical workflows, patient-centered design, and continuous technological evolution. This clarity allows healthcare professionals to differentiate meaningful innovation from consumer-grade technology lacking clinical evidence. The chapter also critically examines what Digital Medicine is not, dispelling confusion about wellness apps, general IT systems, and unregulated digital tools. The goal is to equip practitioners to prioritize safety, efficacy, and clinical relevance when evaluating digital solutions. The narrative then explores why Digital Medicine matters—as a toolkit for clinicians and as a societal shift in how health is perceived and managed. The section on empowering patients illustrates how Digital Medicine supports real-time monitoring, informed self-management, and equitable access to care. It showcases how AI-driven apps and wearable technologies promote active participation and personalized interventions, aligning with the “P4 Medicine” model (Predictive, Preventive, Personalized, Participatory).