Can every convex polyhedron be cut along its edges and unfolded into one connected piece without overlap?
This problem arguably dates back to the 1500s, although it was first posed formally by Shephard in 1975 (although it arguably dates back to the 1500s). There are also many related unfolding (un)folding problems which are still open, see http://maven.smith.edu/~orourke/TOPP/P9.html#Problem.9

