This project work contains two parts: sobolev spaces and application to elliptic partialrndifferential equations. The theory of sobolev space has been originated by RussianrnmathematicsrnS.L sobolev around 1938. These spaces were not introduced for some theoreticalrnpurpose,rnbut for the need of the theory of partial differential equations.rnThis paper is then aimed at showing the applications of sobolev spaces defined inrnspaces, solving Dirichlet problems for the poisson equations, and the Dirichlet problemsrnwith spectral parameters