Electronic Journal of Differential Equations, Vol. 2012 (2012), No. 10, pp. 1-14. Title: Real interpolation spaces between the domain of the Laplace operator with transmission conditions and L^p on a polygonal domain Authors: Aissa Aibeche (Univ. de Setif, Algeria) Wided Chikouche (Univ. de Setif, Algeria) Yasmina Daikh (Universite de Jijel, Algeria) Abstract: We provide a description of the real interpolation spaces between the domain of the Laplace operator (with transmission conditions in a polygonal domain $\Omega$) and $L^p(\Omega)$ as interpolation spaces between $\mathcal{W}^{2,p}(\Omega)$ (possibly augmented with singular solutions) and $L^p(\Omega)$. This result relies essentially on estimates on the resolvent and the reiteration theorem. Submitted April 10, 2011. Published January 13, 2012. Math Subject Classifications: 35R05, 35A20, 46B70. Key Words: Transmission problem; non-smooth domains; interpolation.