Abstract: The present invention provides catalyst systems useful in the polymerization of olefins comprising a transition metal component and a ligand component comprising a Nitrogen atom and/or functional groups comprising a Nitrogen atom, generally in the form of an imine functional group. In certain embodiments, the ligand component may further comprise a phosphorous atom. Preferred ligand components are bidentate (bind to the transition metal at two or more sites) and include a nitrogen-transition metal bond. The transition metal-ligand complex is generally cationic and associated with a weakly coordinating anion. In a preferred embodiment, the catalyst system of the present invention further comprises a Lewis or Bronsted acid complexed with the ligand component of the transition metal-ligand complex.