This chapter presents knowledge concerning the effects of urban trees and forests on urban microclimate variables and human thermal comfort. Benefits of urban vegetation are evidenced by the growing interest on urban tree planting as an energy use control during summer. The chapter is divided into three sections. The first is dedicated to the effect of urban trees and forest on air temperature and its variability. The second assesses the effect of urban tree and forest on energy exchange and thus on surface temperature and mean radiant temperature. The last section presents an analysis of the effect of microclimate interventions with trees on weather parameters and human thermal comfort.