Urban density is a term used in urban planning and urban design to refer to the number of people inhabiting a given urbanized area. As such it is to be distinguished from other measures of population density. Urban density is considered an important factor in understanding how cities function. Research related to urban density occurs across diverse areas, including economics, health, innovation, psychology and geography as well as sustainability.

It is commonly asserted that higher density cities are more sustainable than low density cities. Much planning theory, particularly in North America, the UK, Australia and New Zealand has been developed premised on raising urban densities, such as New Urbanism, Transit-oriented development, and Smart growth.

However, the link between urban density and aspects of sustainability remains a contested area of planning theory^{[citation needed]}. Many^[who?] experts on sustainable urbanism, including prominent urban designer Jan Gehl, argue that low-density, dispersed cities are unsustainable as they are automobile dependent. A minority, such as Randy O'Toole, author of Gridlock and a senior fellow at the Cato Institute, counter that raising densities results in more expensive real estate, greater road congestion and more air pollution. At a broader level though, there is evidence to indicate a strong negative correlation between the total energy consumption of a city and its overall urban density, i.e. the lower the density, the more energy consumed.

Arif Hasan, is a Pakistani architect, planner, teacher, social researcher, and writer. He is a recipient of Hilal-i-Imtiaz, the country's highest award for its citizens.

Hasan studied architecture at Oxford Polytechnic (now Oxford Brookes University), UK from 1960 to 1965.

In 1968, he started his own practice in Karachi.

He has been involved with the Orangi Pilot Project (OPP), Karachi since 1982. In 1989, he founded the Urban Resource Centre (URC) in Karachi of which he is the founder chairman.

Winy Maas (born 1958, Schijndel) is a Dutch architect, landscape architect, professor and urbanist. In 1991 together with Jacob van Rijs and Nathalie de Vries he set up MVRDV. Early work such as the television centre Villa VPRO and the housing estate for elderly WoZoCo, both in the Netherlands, have brought him international acclaim and established MVRDV’s leading role in international architecture. Winy Maas is married to Mirjam Veldhuijzen van Zanten (born 1964, Enter) she is a stage director, they have 3 children.

He completed his studies at the RHSTL Boskoop, graduating as a "landscape architect", and in 1990 he got his degree from the Delft University of Technology. He currently is visiting professor of architectural design at the Massachusetts Institute of Technology and is professor in architecture and urban design at the faculty of architecture, Delft University of Technology. Before this he was professor at among others Berlage Institute, Ohio State and Yale University.

In 1991, together with Jacob van Rijs and Nathalie de Vries, he founded the MVRDV studio (an acronym of the initials of the names of the three founders), which produces designs and studies in the fields of architecture, urban studies and landscape design. The studies on light urbanism for the City of Rotterdam, the headquarters of the Dutch Public Broadcasting Company VPRO and the Wozoco's senior citizens' residences in Amsterdam, which won the J.A. van Eck Prize of the Dutch Architects' Association, have brought MVRDV to the attention of a vast collection of clients, giving the studio international renown. Today, the studio is actively involved in numerous projects in various parts of the world. MVRDV designed the Dutch pavilion for Expo 2000 in Hanover, the Logrono Eco-City in Spain, the Gyre building in Tokyo and many others.