The pursuit of sustainable urban development demands professionals who can work across disciplinary boundaries and adapt planning practices to future environmental and social challenges. Such expertise requires an understanding of the complex interactions within urban spaces and planning systems to create conditions that enhance quality of life while supporting efficiency, equity, democratic values, and long-term sustainability. Urban planning and design therefore combine theoretical knowledge with practical skills drawn from architecture, planning, and environmental science. Sustainability has become a central concern for contemporary urban planners, as modern lifestyles increasingly strain natural resources, damage ecosystems, widen social inequalities, intensify urban heat, and contribute to climate change. In response, many planners promote sustainable city models that seek to balance development with ecological and social responsibility. Although widely discussed today, sustainable urban development remains a relatively recent and sometimes contested concept. Scholars describe sustainable urban development as an approach that strengthens the long-term social and environmental health of cities and towns. Key principles include compact urban form, efficient land use, accessible transportation, responsible resource management, reduced pollution and waste, restoration of natural systems, quality housing, community participation, and preservation of cultural heritage. Given the complexity of political and governance structures, effective implementation requires broad institutional and public support. This encyclopaedia examines the major issues of urban planning and design and serves as a valuable reference for students, researchers, and professionals in architecture, planning, and environmental sciences.