  In this article, the authors study the interpolation of Morrey-Campanato
spaces and some smoothness spaces based on Morrey spaces, e.\,g., Besov-type
and Triebel-Lizorkin-type spaces. Various interpolation methods, including the
complex method, the $\pm$-method and the Peetre-Gagliardo method, are studied
in such a framework. Special emphasize is given to the quasi-Banach case and to
the interpolation property.
