Photoaddressable polymers (PAPs) are side-chain copolymer systems functionalized with azobenzene chromophores and mesogenic side groups. They show very large birefringence values after illumination with polarized light. The molecular mechanisms involved are photoinduced isomerization cycles of the azo side groups, which induce strong molecular reorientations (cooperative motion of light-absorbing azobenzene chromophores and non-absorbing mesogenic groups). Due to the long-term and high-temperature stability of their light-induced birefringence, PAPs are very promising recording materials for optical data storage applications such as high-capacity DVDs and holographic memory.