  We prove interpolation estimates between Morrey-Campanato spaces and Sobolev
spaces. These estimates give in particular concentration-compactness
inequalities in the translation-invariant and in the translation- and
dilation-invariant case. They also give in particular interpolation estimates
between Sobolev spaces and functions of bounded mean oscillation. The proofs
rely on Sobolev integral representation formulae and maximal function theory.
Fractional Sobolev spaces are also covered.
