A sustainable city is a city designed with consideration of environmental impact. Field of industrial ecology is sometimes used in planning these cities. Generally, developmental experts agree that a sustainable city should meet the needs of the present without sacrificing the ability of future generations to meet their own needs.

Ideally, a sustainable city creates an enduring way of life across the four domains of ecology, economics, politics and culture. Due to proximity of people and resource, it is possible to save energy for transportation, mass transit systems and resources such as food.

The ecological cities are achieved through various means, such as agricultural systems, renewable energy, heat island effect, public transport, urban heat islands, urban sprawl, smart growth, green roofs, and key performance indicators for city administrators.

As the major focus of the sustainable cities, sustainable transportation attempts to reduce a city’s reliance and use of greenhouse emitting gases by utilizing eco friendly urban planning, low environmental impact vehicles, and residential proximity.

Due to the significant impact that transportation services have on a city’s energy consumption, the last decade has seen an increasing emphasis on sustainable transportation by developmental experts. Currently, transportation systems account for nearly a quarter of the world’s energy consumption and carbon dioxide emission.

The Carbon Trust states that there are three main ways cities can innovate to make transport more sustainable without increasing journey times - better land use planning, modal shift to encourage people to choose more efficient forms of transport, and making existing transport modes more efficient.

The concept of car free cities or a city with large pedestrian areas is often part of the design of a sustainable city. The concept of urban proximity is an essential element of current and future sustainable transportation systems.

There are 13 global challenges to establishing sustainable cities: demographic change and migration, globalization of the job market, poverty and unmet Millennium Development Goals, segregation, spatial patterns and urban growth, Metropolization and the rise of urban regions, more political power for local authorities, new actors for developing a city and providing services, decline in public funding for development, the environment.