Darboux transformations for linear operators on two-dimensional regular lattices

Darboux transformations for linear operators on regular two-dimensional lattices are reviewed. The six-point scheme is considered as the master linear problem, whose various specifications, reductions and sublattice combinations lead to other linear operators together with the corresponding Darboux transformations. The second part of the review deals with multidimensional aspects of (basic reductions of) the four-point scheme, as well as the three-point scheme.