The Mobius strip, obtained by taking a rectangular strip of plastic or paper, twisting one end through 180 degrees, and then joining the ends, is the canonical example of a one-sided surface. Finding its characteristic developable shape has been an open problem ever since its first formulation in refs 1,2. Here we use the invariant variational bicomplex formalism to derive the first equilibrium equations for a wide developable strip undergoing large deformations, thereby giving the first nontrivial demonstration of the potential of this approach. We then formulate the boundary-value problem for the Mobius strip and solve it numerically. Solutions for increasing width show the formation of creases bounding nearly flat triangular regions, a feature also familiar from fabric draping(3) and paper crumpling(4,5). This could give new insight into energy localization phenomena in unstretchable sheets(6), which might help to predict points of onset of tearing. It could also aid our understanding of the relationship between geometry and physical properties of nano-and microscopic Mobius strip structures(7-9).