Urban areas are generally warmer than non-built-up areas. These local differences in temperature are mainly determined by the building materials' ability to absorb and store heat and how high and close together the buildings are. Other important determinants are the amount of impermeable surfaces (i.e. roads, sidewalks, parking lots and roofs) and the quantities of anthropogenic heat and air pollution released. During the day, differences in air temperature are relatively small, but on clear, calm nights temperature differences of up to several degrees may occur between urban and rural areas, as well as between different built-up areas/land uses. The socio-economic and health impacts of urban climate conditions can be both positive and negative. In winter, the urban climate conditions decrease heating demand in buildings, maintenance of roads and roofs (i.e. ploughing, salting and sanding) and cold stress. However, in summer the urban climate conditions increase cooling demand in buildings and heat stress. In an era of changeable climate, with higher temperatures and more frequent, longer and more intense heat waves, there is a growing need to cool our cities. One effective measure to reduce temperature and create shade during long hot periods is to increase the amount of vegetation, i.e. construct parks, green roofs and facades, and plant trees. Another measure to reduce the temperature is to use highly reflective surfaces and materials and by doing so decrease the heat stored in buildings and surfaces. This report, which is based on a literature review, describes the climate conditions typical of a city and the processes behind them, their socio-economic and health impacts, and a number of different measures to reduce the temperature in a city.