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Urban Heat Island (UHI) as a consequence of urbanization was first documented by Howard when he was investigating the climate of London in 1818.This study is carried to summarize the formation and mitigation of UHI.It also concludes the review of the techniques used to study UHI.UHI is the mutual response of many controllable (sky view factor, green area, building material and anthropogenic heat sources) and uncontrollable (Wind speed, cloud cover and season) factors.Urban Heat Island Intensity (UHII) as an indicator of evaluating the severity of the urbanization of an area is defined as the spatially-averaged temperature difference between urban and its surrounding rural area.The adverse impacts of UHI include the deterioration of living environment, increase in energy consumption, elevated emission of air pollutants and greenhouse gases and even an increase in mortality rates.Based on the literature review, the possible mitigating measures can broadly be categorized as: (1) related to reducing anthropogenic heat release;(2) related to better design and planning of urban infrastructures (e.g.building materials and sky view factor);(3) additional design factors (e.g.green areas and spray cooling technologies).In recent years, three main observational approaches are applied in urban heat island studies: field measurement, thermal remote sensing and small-scale modeling.In the field measurement approach, the analysis of statistic on urban-rural differences based on groups of fixed stations or mobile stations.However, the installation of measurement devices around a city is a quite expensive and time-consuming task.Under the support of satellite, airborne and aircraft platforms, thermal remote sensing technology can observe UHI through measuring the resultant surface temperature which contains the effects of surface radiative and thermodynamic properties.In small scale modeling approach, the urban area is mostly replaced with prototype on obeying the similarity theory with real case.