A foldable electronic device , comprising: a first support structure (12-1); a second support structure (12-2); a flexible display that has a first portion supported by the first support structure (12-1) and a second portion supported by the second support structure (12-2) and that is configured to bend bunds as the first (12-1) and second (12-2) 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 (100-1), and a second hinge portion (100-2); wherein the first hinge portion (100-1) includes first and second gears and a first linkage member configured to hold the first gear of the first hinge portion (100-1) against the curved toothed surface of the toothed member while the first gear of the first hinge portion (100-1) walks along the curved toothed surface , and the second hinge portion (100-2) includes first and second gears and a second linkage member configured to hold the first gear of the second hinge portion (100-2) against the curved toothed surface of the toothed member while the first gear of the second hinge portion (100-2) walks along the curved toothed surface ; and wherein the second gear of the first hinge portion (100-1) is fixedly attached to the first support structure (12-1), has teeth that engage the teeth of the first gear of the first hinge portion (100-1), and does not rotate relative to the first support structure (12-1) during the folding and unfolding of the flexible display , and the second gear of the second hinge portion (100-2) is fixedly attached to the second support structure (12-2), has teeth that engage the teeth of the first gear of the second hinge portion (100-2), and does not rotate relative to the second support structure (12-2) during the folding and unfolding of the flexible display . a first support structure (12-1); a second support structure (12-2); a flexible display that has a first portion supported by the first support structure (12-1) and a second portion supported by the second support structure (12-2) and that is configured to bend bunds as the first (12-1) and second (12-2) 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 (100-1), and a second hinge portion (100-2); wherein the first hinge portion (100-1) includes first and second gears and a first linkage member configured to hold the first gear of the first hinge portion (100-1) against the curved toothed surface of the toothed member while the first gear of the first hinge portion (100-1) walks along the curved toothed surface , and the second hinge portion (100-2) includes first and second gears and a second linkage member configured to hold the first gear of the second hinge portion (100-2) against the curved toothed surface of the toothed member while the first gear of the second hinge portion (100-2) walks along the curved toothed surface ; and wherein the second gear of the first hinge portion (100-1) is fixedly attached to the first support structure (12-1), has teeth that engage the teeth of the first gear of the first hinge portion (100-1), and does not rotate relative to the first support structure (12-1) during the folding and unfolding of the flexible display , and the second gear of the second hinge portion (100-2) is fixedly attached to the second support structure (12-2), has teeth that engage the teeth of the first gear of the second hinge portion (100-2), and does not rotate relative to the second support structure (12-2) during the folding and unfolding of the flexible display . <EOS>