An involuted orbifold MSSM

A compactification of the E_8 x E_8 heterotic string on a Z_2 x Z_2 orbifold equipped with an additional freely acting involution is presented. This model reproduces the exact chiral MSSM spectrum with matter parity and a non-trivial Yukawa structure. The key ingredient is a freely acting Wilson line associated to the involution, breaking SU(5) to SU(3) x SU(2) x U(1)_Y. This work is based on a talk given at the "9th Hellenic School and Workshop on Elementary Particle Physics and Gravity" and reviews the results of a collaboration with M. Blaszczyk, S. Groot Nibbelink, M. Ratz, F. Ruehle and M. Trapletti.