Electronic Journal of Differential Equations, Vol. 2010(2010), No. 60, pp. 1-13. Title: Maximum principle and existence results for elliptic systems on R^N Authors: Liamidi Leadi (Univ. d'Abomey Calavi, Benin) Aboubacar Marcos (Univ. d'Abomey Calavi, Benin) Abstract: In this work we give necessary and sufficient conditions for having a maximum principle for cooperative elliptic systems involving p-Laplacian operator on the whole $\mathbb{R}^{N}$. This principle is then used to yield solvability for the cooperative elliptic systems by an approximation method. Submitted June 5, 2009. Published May 05, 2010. Math Subject Classifications: 35B50, 35J20, 35J55. Key Words: Principal and nonprincipal eigenvalues; elliptic systems; p-Laplacian operator; approximation method.