The aim of this paper is to obtain new necessary and sufficient conditions for the uniform exponential stability of variational difference equations with applications to robustness problems. We prove characterizations for exponential stability of variational difference equations using translation invariant sequence spaces and emphasize the importance of each hypothesis. We introduce a new concept of stability radius r stab A; B, C for a variational system of difference equations A with respect

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... o a perturbation structure B, C and deduce a very general estimate for the lower bound of r stab A; B, C . All the results are obtained without any restriction concerning the coefficients, being applicable for any system of variational difference equations.