NOVELTY - A cyclic olefin copolymer has repeating unit (A) derived from olefin(s) (I) and repeating unit (B) derived from cyclic non-conjugated diene (II-IV). The molar ratio of the repeating units (A, B) is 40/60-80/20.    USE - Cyclic olefin copolymer used for forming molded product e.g. film, sheet, circuit board and substrate for liquid crystal display (all claimed). Uses include but are not limited to optical fiber, optical waveguide, light filter, lens, base material for solar cell, semiconductor element, coating material of electronic device, hybrid integrated circuit, layer insulation material and adhesive agent.    ADVANTAGE - The cyclic olefin copolymer crosslinks with high density and provides crosslinked material having excellent heat resistance, mechanical characteristics, dielectric characteristics, transparency, gas barrier property and workability.    DETAILED DESCRIPTION - A cyclic olefin copolymer has repeating unit (A) derived from olefin(s) of formula (I) and repeating unit (B) derived from cyclic non-conjugated diene chosen from formulae (II-IV). The molar ratio of the repeating units (A, B) is 40/60-80/20.    R300=H or optionally branched 1-29C hydrocarbyl;    u,w=0 or 1;    v=0 or more;    R1-R16,Ra,Rb=H, halo, 1-20C (halo)alkyl, 3-15C cycloalkyl or 6-20C aromatic hydrocarbyl;    R102-R104=H or 1-10C alkyl;    or R15+R16=mono- or poly-cyclic ring;and    t=0-10.    INDEPENDENT CLAIMS are included for the following:    (1) manufacture of the cyclic olefin copolymer, which involves addition polymerizing olefin of formula (Ia) and cyclic olefin chosen from formulae (IIa-IVa) in presence of transition metal compound of formula (IX) and catalyst component (M) containing organometallic compound, organo aluminoxy compound or the transition metal compound which forms ion pair;    (2) varnish, which contains the cyclic olefin copolymer and organic solvent; and    (3) crosslinked material, which is obtained by crosslinking the cyclic olefin copolymer.    M=3-11 groups transition metal;    m=1-4;    R1'-R6'=H, halo, hydrocarbyl, heterocyclic compound residue, oxygen-, nitrogen-, boron-, sulfur-, phosphorus-, silicon-, germanium- or tin-containing group;    n=valence of M;and    X=H, halo, hydrocarbyl, oxygen-, nitrogen-, boron-, sulfur-, aluminum-, halogen-, phosphorus-, silicon-, germanium- or tin-containing group, or heterocyclic compound residue.