I’ll introduce an extension of the Chern-Simons form, associated to a path of connections on a bundle over a manifold M, to a differential form on the free loop space LM. This form determines an equivalence relation on the set of connections on a bundle, and can be used to define a functor from manifolds to rings, in much the same way that diﬀerential K-theory is deﬁned by Simons and Sullivan using the Chern-Simons form. This ring, loop diﬀerential K-theory, yields a reﬁnement of diﬀerential K-theory, and in particular includes holonomy information in its classes. Additionally, loop diﬀerential K-theory is strictly coarser than the Grothendieck group of bundles with connection up to gauge equivalence. This is joint work with Thomas Tradler and Mahmoud Zeinalian.