The main tools of Mathematical Morphology are a broad class of nonlinear image operators. They can be defined in terms of algebraic set operators or as Partial Differential Equations (PDEs). We propose a framework of partial difference equations on arbitrary graphs for introducing and analyzing morphological operators in local and non local configurations. The proposed framework unifies the classical local PDEsbased morphology for image processing, generalizes them for non local configurations and extends them to the processing of any discrete data living on graphs.