The copolymerization of ethene with norbornene derivatives, as well as their terpolymerization with 1-alkenes, using a series of neutral, square-planar nickel complexes containing anionic P∼O chelates is described. In copolymerizations, up to 50 mol % incorporation of norbornene, leading to an essentially alternating copolymer, is obtained. With norbornene derivatives bearing oxygen functionalities, the level of incorporation is lower, as are the reaction rates and polymer molecular weights. In the case of terpolymerization of ethene and norbornene with 1-alkenes, the polymer molecular weights tend to be low because of slower monomer insertion and additional chain-transfer pathways that are available following 1-alkene insertion. For the ethene/norbornene polymers synthesized, the glass transition temperature (Tg) increases smoothly with increasing norbornene content. Solution-cast films of the polymers show good optical clarity.