Binney, J. 1992, Ann. Rev. Astr. Ap. 30, 51.

The available observational data on warping are briefly reviewed. The data demonstrate that HI disks are usually warped and that the warp becomes pronounced at the edge of the optical image. The naive theory is examined in an attempt to explain the observations. Attention is also given to waves and modes in disks, the halo's response and dissipation, warps and galaxy formation, warps and infall, and tidally generated warps.