Olefin metathesis step-growth (acyclic diene metathesis (ADMET)) and chain-growth (ring-opening metathesis) polymerization was used to prepare linear poly(phosphonate)s with variable hydrophilicity. The first phosphonate monomer, i.e., di(undec-10-en-1-yl) methylphosphonate, for ADMET polymerization was developed, and potentially degradable and biocompatible, unsaturated poly(phosphonate)s were prepared with molecular weights up to 23 000 g mol -1 with molecular weight dispersities D < 2. These polymers were studied with respect to their interaction with a calcium phosphate bone substitute material from an aqueous nanoparticle dispersion that was prepared by a solvent evaporation miniemulsion protocol. Ring-opening metathesis polymerization (ROMP) was employed to synthesize more hydrophilic amorphous polyphosphonates from a novel seven-membered cyclic phosphonate monomer, i.e., 2-methyl-4,7-dihydro-1,3,2-dioxaphosphepine 2-oxide, as well as hydrophobic crystalline copolymers with cis-cyclooctene. ROMP yielded polymers with molecular weights up to 6000 g mol-1 (homopolymer) and 47 000 g mol-1 (copolymers). Poly(phosphonate)s are potentially hydrolytically degradable materials and therefore promising materials for biomedical applications.