Add to ORKGALFA is the detector for the Absolute Luminosity measurement For Atlas. A basic information about luminosity & different luminosity measurements is given in the first part. Technical details concerning ALFA are explained in the second part. The key use of ALFA for the luminosity measurement is subject of the third part. The fourth part is devoted to the possibility of using ALFA for the single diffraction measurement. Finally, the actual status of the ALFA detector is summarized in the conclusion