A window includes a plurality of transparent substrates spaced apart from each other in a thickness direction; a light transmittance-adjusting layer on a surface of at least one transparent substrate of the plurality of transparent substrates and having a thermochromic or thermotropic characteristic; and an air circulator configured to circulate a heat transfer medium in a space between the plurality of transparent substrates for changing a light transmittance of the light transmittance-adjusting layer.