  We review and then combine two aspects of the theory of bundle gerbes. The
first concerns lifting bundle gerbes and connections on those, developed by
Murray and Gomi. Lifting gerbes represent obstructions against extending the
structure group of a principal bundle. The second is the transgression of
gerbes to loop spaces, initiated by Brylinski and McLaughlin and with recent
contributions of the author. Combining these two aspects, we obtain a new
formulation of lifting problems in terms of geometry on the loop space. Most
prominently, our formulation explains the relation between (complex) spin
structures on a Riemannian manifold and orientations of its loop space.
