  We present a finite-dimensional and smooth formulation of string structures
on spin bundles. It uses trivializations of the Chern-Simons 2-gerbe associated
to this bundle. Our formulation is particularly suitable to deal with string
connections: it enables us to prove that every string structure admits a string
connection and that the possible choices form an affine space. Further we
discover a new relation between string connections, 3-forms on the base
manifold, and degree three differential cohomology. We also discuss in detail
the relation between our formulation of string connections and the original
version of Stolz and Teichner.
