The mitigation of the heat island effect can be achieved by the use of cool materials that arecharacterized by high solar reflectance and infrared emittance values. Several types of cool coatings,both commercially available and prototype ones have been tested. Their spectral reflectance, infraredemittance and surface temperature measurements reveal that these materials can be classified ascool materials with the ability to maintain lower surface temperatures. Cool materials can be used onbuildings (roofs and walls) and other surfaces of the urban environment. Based on these results, amodeling study has been undertaken to assess the Urban Heat Island effect over Athens, Greece, adense populated city, trying to analyze the impacts of large-scale increases in surface albedo onambient temperature. Numerical simulations were performed by the urbanized version of the nonhydrostaticPSU/NCAR Mesoscale Model (MM5, version V3-6-1). Two scenarios of modified albedowere studied a moderate and a high increase in albedo scenario. It was found that large-scaleincreases in albedo could lower ambient air temperatures by 2C. The results of this study can help topromote the adoption of high albedo measures in building energy codes and urban planningregulations.