Urbanization and burgeoning population in the Phoenix metropolitan area has led to rapid development of engineering infrastructure, which, in turn, has led to a significant urban heat island (UHI). During the daytime, built surfaces absorb heat, and their high thermal capacities and special surface properties cause retention of heat within the material for periods longer than that of natural surfaces. In addition, anthropogenic activities (e.g. air conditioning, motor vehicle traffic) emit substantial amounts of heat to the urban atmosphere, causing a positive feedback on UHI. For example, during hotter outdoor conditions on summer nights, air conditioner usage drastically increases, which in turn increases outdoor temperature and energy consumption. Urban Air pollution also exacerbates the UHI, either because outgoing radiation from urban surfaces is reflected back from pollutants or contaminants such as ozone can absorb radiation, thus trapping heat (Urban Greenhouse Effect). Lighter winds of dense urban areas can reduce cooling and trap pollutants, and hence exacerbate UHI. All of these factors are colluding in the Phoenix area to produce its Urban Heat Island, which can be as high as 10-11 degrees on summer days. The socio-economic outcomes of UHI are suspected to threaten the sustainability of the area, calling for implementation of strong heat island mitigation strategies. This presentation deals with observations and modeling of UHI in Phoenix, and will describe how UHI can even lead to a shift of wind regimes in the area that may alter pollution dispersion patterns.