Basic oxygen furnace (BOF)-slag represents a valuable secondary raw-material which is mainly used for road construction. The quality requirements for BOF-slags are getting stricter and therefore it is necessary to distinguish between the slags which are allowed for the further use and which need to be deposited. In Linz the selection of BOF-slag is carried out by a Laser Induced Breakdown Spectroscopy (LIBS)-plant. The criteria for the selection of road construction material depends on volume stability and environmental limits for harmful elements. The LIBS plant is a Laser spectroscopy system in industrial scale which determines the chemical composition of BOF-slag. One part of the work was an extensive literature study which was carried out for a better understanding of BOF-slag as secondary raw-material. The metallurgical background of the BOF-process was described, especially the slag formations and the tasks of the slag. Alternative recycling routes respectively applications for BOF-slag are also presented. The mineralogy of BOF-slag and the background of volume stability of a slag are also described in the work. Moreover, different possibilities to improve the quality of slags are introduced. The legal provisions for the use of BOF-slag in different countries and in particular in Austria were determined. The LIBS-technology was explained in detail based on the LIBS-plant in Linz. At last the whole processing of BOF-slag at voestalpine in Linz is introduced, starting from the racking at the BOF and ending with the final product as aggregate. An experimental campaign was carried out to optimize the measurement accuracy of the LIBS-system and the limits for road construction material were settled by the help of these results. Besides that, investigations were carried out concerning different cooling conditions of BOF-slags. The different phase formations of all slags were researched in industrial scale. Finally thermodynamic calculations were made with the software FactSageTM.