A foldable electronic device, comprising: a first support structure; a second support structure; a flexible display that has a first portion supported by the first support structure and a second portion supported by the second support structure and that is configured to bend bunds as the first and second support structures rotate relative to each other during folding and unfolding of the flexible display; and a hinge having a toothed member with a curved toothed surface, a first hinge portion, and a second hinge portion; wherein the first hinge portion includes first and second gears and a first linkage member configured to hold the first gear of the first hinge portion against the curved toothed surface of the toothed member while the first gear of the first hinge portion walks along the curved toothed surface, and the second hinge portion includes first and second gears and a second linkage member configured to hold the first gear of the second hinge portion against the curved toothed surface of the toothed member while the first gear of the second hinge portion walks along the curved toothed surface; and wherein the second gear of the first hinge portion is fixedly attached to the first support structure, has teeth that engage the teeth of the first gear of the first hinge portion, and does not rotate relative to the first support structure during the folding and unfolding of the flexible display, and the second gear of the second hinge portion is fixedly attached to the second support structure, has teeth that engage the teeth of the first gear of the second hinge portion, and does not rotate relative to the second support structure during the folding and unfolding of the flexible display. a first support structure; a second support structure; a flexible display that has a first portion supported by the first support structure and a second portion supported by the second support structure and that is configured to bend bunds as the first and second support structures rotate relative to each other during folding and unfolding of the flexible display; and a hinge having a toothed member with a curved toothed surface, a first hinge portion, and a second hinge portion; wherein the first hinge portion includes first and second gears and a first linkage member configured to hold the first gear of the first hinge portion against the curved toothed surface of the toothed member while the first gear of the first hinge portion walks along the curved toothed surface, and the second hinge portion includes first and second gears and a second linkage member configured to hold the first gear of the second hinge portion against the curved toothed surface of the toothed member while the first gear of the second hinge portion walks along the curved toothed surface; and wherein the second gear of the first hinge portion is fixedly attached to the first support structure, has teeth that engage the teeth of the first gear of the first hinge portion, and does not rotate relative to the first support structure during the folding and unfolding of the flexible display, and the second gear of the second hinge portion is fixedly attached to the second support structure, has teeth that engage the teeth of the first gear of the second hinge portion, and does not rotate relative to the second support structure during the folding and unfolding of the flexible display.