With the increasing number of large scale assessments (LSA) the question arises, how far these studies measure similar constructs and whether it is possible to link the results of national and international studies. This article provides an overview on the methodical procedures when analyzing the conceptual and dimensional equivalence of different LSA and describes methodical approaches of linking measurement scales from different studies. Besides that we provide an overview on actual linking studies. With regard to this background the results of the three studies in this special issue will be summarized.