Endohedral complexes of fullerenes are some of the most attractive targets of research in fullerene chemistry and physics. An overview of the field is provided with a focus on endohedral complexes incorporating lanthanide metals, noble gases, and atomic nitrogen. Although the present approaches have been successful in providing the first members of this class of fullerenes, their preparation is still difficult and limited to a few elements. It is argued that ring opening reactions within fullerene shells have the potential to provide easy access to endohedral metallofullerenes on a large scale, including those with transition metals which are potentially the most interesting elements in regard to their materials properties. Current ring opening reactions within fullerene shells are reviewed. An outlook on ring opening reactions leading to effectively large apertures is presented.

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