Urban development in the twenty-first century is increasingly defined by a dual challenge: cities must absorb continued demographic growth while reducing environmental burdens and restoring the social value of public space. A human-scale response to this challenge is found in active mobility (AM), understood as walking and cycling supported by appropriate urban form, public infrastructure, and digital coordination. This article presents a structured conceptual synthesis of AM through the framework of ecosystemic urbanism (EU), positioning the discussion squarely within the concerns of urban development and smart-city governance. The analysis draws on the four principal axes of EU—compactness and functionality, complexity, efficiency, and social cohesion—and the seven contrasting binomials that clarify the tensions between sustainable and car-dependent urbanization. The paper further integrates the five levels of walking needs (feasibility, accessibility, safety, comfort, and pleasurability) and the four social facilitators of meaning-making in movement (breadth of experience, identity expression, pausability, and collaborative creativity). The synthesis shows that active mobility supports compact urban forms, reduces sprawl, improves multimodal accessibility, strengthens environmental performance, and expands opportunities for social exchange. It also demonstrates that digital tools can amplify the benefits of AM through hyperconnectivity and last-mile coordination, provided they are anchored in equitable and legible public space. By reframing active mobility as an urban development strategy rather than a narrow transport option, the article offers a coherent planning argument for neighborhood regeneration, public-space reallocation, climate resilience, and inclusive smart-city transformation.