As global urbanization accelerates, cities face unprecedented challenges in maintaining sustainability while accommodating growing populations. Urban areas already account for approximately 75% of global energy consumption and 80% of greenhouse gas emissions, despite occupying only 3% of Earth's land surface. This concentration of environmental impact has prompted urban planners and policymakers to develop innovative strategies for sustainable city development. Green infrastructure has emerged as a crucial component of these strategies. This approach incorporates natural elements into urban design, including green roofs, vertical gardens, and urban forests. These features provide multiple benefits: they reduce the urban heat island effect, manage stormwater runoff, improve air quality, and enhance residents' mental well-being. Singapore's "City in a Garden" initiative exemplifies this approach, transforming the city-state into a model of urban sustainability. Furthermore, sustainable transportation systems are essential for reducing urban carbon footprints. Cities like Copenhagen and Amsterdam have invested heavily in cycling infrastructure, achieving remarkable modal shifts away from private automobiles. Smart city technologies also play an increasingly important role, utilizing data analytics and Internet of Things devices to optimize resource consumption, traffic flow, and waste management. However, the transition to sustainable cities requires more than technological solutions; it demands fundamental changes in urban governance, citizen behavior, and economic models that prioritize long-term environmental health over short-term gains.