Cyclodextrins (CDs) form inclusion complexes with various polymers with high selectivities to give crystalline compounds. alpha-CD formed complexes with poly(ethylene glycol) (PEG) and oligoethylene in high yields, although beta-CD did not form complexes with PEG. However, beta-CD formed complexes with poly(propylene glycol) (PPG), Although alpha-CD did not form complexes with polyisobutylene (PIE) and poly(methyl vinyl ether) (PMVE), gamma-CD formed complexes with PIE and PMVE, There is a good correlation between the sectional areas of the polymers and the sizes of the CDs. The stoichiometries, properties, and structures of the complexes are discussed. The yield of the complexes increased with increasing molecular weight. Polyrotaxanes, in which many cyclodextrins are threaded on a poly(ethylene glycol) chain, were prepared by capping the chain ends of the polymers in the complexes with bulky groups.