A flexible display device includes a flexible display panel and a window member. The flexible display panel includes a folding area, and a peripheral area disposed adjacent to the folding area. The window member includes a first base layer on the flexible display panel, and a second base layer having a substantially same modulus as that of the first base layer. A first thickness portion of the second base layer, which overlaps the folding area, has a thickness smaller than a thickness of a second thickness portion of the second base layer, which overlaps the peripheral area.