Flexible window and flexible display device including the same

A flexible window includes: a first film layer through which light is incident to the flexible window from a display panel of a flexible display device, the first film layer including: a plurality of stacked first sub-film layers, an adhesive layer disposed between adjacent first sub-film layers, and an index matching layer disposed between a first sub-film layer and the adhesive layer adjacent thereto; and a second film layer on the first film layer to be disposed further from the display panel than the first film layer, the second film layer having a Young's modulus lower than that of each of the first sub-film layers. Within the flexible window, a refractive index of the index matching layer has a value between a refractive index of each of the first sub-film layers and a refractive index of the adhesive layer.