Abstract: Contact lenses comprising hydrophilic units of which the only or major proportion are derived from an N-vinyl heterocyclic monomer hydrophobic units derived from a hydrophobic monomer, and allylic cross-linking units containing more than one polymerizable double bond selected from monoallyl itaconate, diallyl itaconate, triallyl cyanurate, triallyl isocyanurate, triallyl trimellitate, N,N-diallylmelamine, other multifunctional allyl monomers formed by the esterification of polybasic acids with allyl alcohol, or mixtures thereof; the proportions of said monomers being adjusted to give the desired water content and resistance to dissolution when the polymer is swollen to equilibrium in an aqueous environment.