We develop the theory of nonlinear localized modes (intrinsic localized mod
es or discrete breathers) in two-dimensional (2D) photonic crystal waveguid
es. We consider different geometries of the waveguides created by an array
of nonlinear dielectric rods embedded into an otherwise perfect linear 2D p
hotonic crystal, and demonstrate that the effective interaction in such wav
eguides is nonlocal, being described by a nonlinear lattice model with long
-range coupling and nonlocal nonlinearity. We reveal the existence of diffe
rent types of nonlinear guided mode that are also localized in the waveguid
e direction, and describe their unique properties, including bistability.