Linked from
The 17 pages that link to Jordan normal form, each with the reason it gives.
Invariant subspaceRelated: Chains of invariant subspaces underlie the block decomposition.
EigenvectorRelated: It describes transformations whose eigenvectors alone do not form a basis.
Square matrixBroader topic: It describes square matrices that cannot be diagonalized.
Jordan decompositionRelated: Its blocks reveal the semisimple and nilpotent contributions directly.