Electronic Journal of Differential Equations, Vol. 2010(2010), No. 02, pp. 1-10. Title: Optimization in problems involving the p-Laplacian Author: Monica Marras (Univ. di Cagliari, Italy) Abstract: We minimize the energy integral $\int_\Omega |\nabla u|^p\,dx$, where $g$ is a bounded positive function that varies in a class of rearrangements, $p>1$, and $u$ is a solution of $$\displaylines{ -\Delta_p u=g \quad\hbox{in } \Omega\cr u=0\quad \hbox{on } \partial\Omega\,. }$$ Also we maximize the first eigenvalue $\lambda=\lambda_g$, where $$ -\Delta_p u=\lambda g u^{p-1}\quad\hbox{in }\Omega\,. $$ For both problems, we prove existence, uniqueness, and representation of the optimizers. Submitted November 2, 2009. Published January 05, 2010. Math Subject Classifications: 35J25, 49K20, 47A75. Key Words: p-Laplacian; energy integral; eigenvalues; rearrangements; shape optimization