Ethylene-norbornene (E-N) copolymers were synthesized with the C-2 metallocene rac-Me2Si(2-Me-[e]-benzindenyl)(2)ZrCl2 (3) and with the constrained geometry Me2Si(Me4CP)((NBu)-Bu-t)TiCl2 (4) in the presence of methylaluminoxane. The E-N copolymerizations were carried out using a variety of monomer feed compositions. Copolymers were fully characterized by C-13 NMR spectroscopy, gel permeation chromatography, and differential scanning calorimetry. Copolymer microstructures were analyzed in detail, through a procedure which accounts for the stoichiometric requirements of the copolymer chain as well as for the measured areas of C-13 NMR signals. This analysis, which quantifies the differences in sequence distribution and tacticity of the polymers, evidenced that mainly alternating stereoregular and stereoirregular copolymers were prepared with 3 and 4, respectively. The copolymer prepared with 4 contains both meso and racemic NEN sequences and small amounts of meso and racemic NN diads, while the alternating copolymer prepared with 3 contains only meso NEN sequences and small amounts of meso NN diads. The formation of NN diads is disfavored with both catalysts. Surprisingly, a significant amount of norbornene (up to similar to 10%) belonging to NNN triads (T) is obtained with the C-2 catalyst.