Since 1985, a large amount of telescope time has been devoted to arc surveys. The strong dependence of lensing on the central mass density explains why the observers concentrated on the richest clusters, either on the basis of large cluster velocity dispersions and galaxy counts, or on the basis of X-ray emission. Without any doubt, this has biased the sample toward optically rich, dense and strong X-ray emitting clusters. Since it is now well established that it is easy to find arc(let)s in this class of clusters, it would be interesting to start a survey for (weak) lensing effects around compact groups and poor clusters of galaxies.
Extensive surveys in rich clusters were initiated by the Toulouse group at CFHT and ESO and Tyson's group at NOAO and CTIO telescopes, followed by the Hawaiian group at CFHT and the UH telescope, and the Durham-Cambridge group at the UKIRT, AAT and WHT telescopes (see Table 1 for references). Most of the observations have been done in the optical range from the B to I bands. However McLaren et al. (1988) observed the arc in A370 in the UV which completed the multi-wavelength observations done on this cluster in the optical and in the infrared (Aragón-Salamanca, Ellis & Sharples 1991; Smail et al. 1993). Up to now, most of the IR observations have been done by Smail et al. (1993) on 7 arcs with known redshifts. The infrared domain should give important insight in the evolution of distant galaxies and could reveal new extremely distant arcs invisible in the optical. It is almost certain that IR surveys of arcs will be a first priority in coming years.