Polymeric materials consisting of an acidic polymer, vinyl ether crosslinker and photoacid generator were found to give positive-working photoresists. An interesting characteristics of the system may be what any polymers having acidic groups as the molecular structure, can be converted to photopolymer only adding vinyl ether crosslinker and PAG. The review will report the examples of the conversion of polymers such as cresol novolak resin, p-hydroxy polystyrene, poly(acrylic acid), and poly(amic acid) to the photosensitive polymers. Among the three components composing the photosensitive polymer, the polymer decides the main characters such as developing agent, optical and mechanical properties. The crosslinker governs the solubility contrast between the polymer layers of the exposed or the unexposed portion. PAG is most important component for this type of photosensitive polymer, because it governs the sensitivity as well as the spectral sensitivity. The photosensitive polymer composed of the poly(amic-acid), divinyl ether crosslinker and PAG gave the patterns, which are very strong against the heat treatment. In the field of nanolithographic patterning, very short wavelength light is used to transfer the patterns of nanometer resolution. For this purpose, the photoresists have to be transparent at 193nm light. Alicyclic compounds containing vinyl ether groups prepared as crosslinker were found to be transparent at 193nm. Several polymers have been synthesized for 193nm lithography. One of those polymers and the alicyclic compound were combined to prepare the photoresist for 193nm lithography. The performance of the photoresist will be also reviewed.