To investigate ultrafast exciton motion, exciton relaxation and related nonlinear optical spectra of photosynthetic antenna systems the dissipative multi-exciton theory is utilized. This type of approach accounts for optically induced transitions to the band of delocaliced single-exciton and two-exciton states as well as takes notice of the coupling to the vibrations of the protein matrix. Different applications are mentioned with emphasis on the Fenna Matthews Olson (FRO) photosynthetic antenna complex of Chlorobium Tepidum.