Itaconic acid, a renewable feedstock obtained by fermentation of carbohydrates, is used as a key substrate to produce aliphatic unsaturated polyesters as well as polynorbornenes. Renewable unsaturated polyesters were prepared by direct polycondensation of dimethyl itaconate (DMI) with diols, whereas the ring-opening-metathesis polymerization (ROMP) of a DMI derived norbornene led to polynorbornenes. The direct polycondensation of DMI was performed with tin(II) ethylhexanoate as catalyst, 4-methoxyphenol as radical inhibitor, and different diols to yield linear unsaturated polyesters with a molecular weight up to 11 500 Da without isomerization or cross-linking of the vinylic double bond. Further modification of the unsaturated polyesters by thia-Michael addition yielded polysulfides, which were subsequently oxidized to polysulfones. Moreover, the solvent-free and straightforward Diels-Alder reaction of DMI and cyclopentadiene was used to prepare a partially renewable norbornene monomer, which was used in ROMP with different catalysts to prepare polymers with low dispersities and adjustable molecular weights. The thereof derived unsaturated and functionalized renewable polynorbornenes were further modified by hydrogenation, and their thermal properties were evaluated.