Vimentin is the major intermediate filament (IF) protein of mesenchymal cells. It shows dynamically altered expression patterns during different developmental stages and high sequence homology throughout all vertebrates, suggesting that the protein is physiologically important. Still, until recently, the real tasks of vimentin have been elusive, primarily because the vimentin-deficient mice were originally characterized as having a very mild phenotype. Recent studies have revealed several key functions for vimentin that were not obvious at first sight. Vimentin emerges as an organizer of a number of critical proteins involved in attachment, migration, and cell signaling. The highly dynamic and complex phosphorylation of vimentin seems to be a likely regulator mechanism for these functions. The implicated novel vimentin functions have broad ramifications into many different aspects of cell physiology, cellular interactions, and organ homeostasis.