This paper summaries studies of the structural geology in and around the island of ¿sp¿ before the excavation of an underground rock laboratory there to explore the problems of storing spent nuclear fuel in Swedish bedrock. Each of the major reorganizations of the plate boundaries around the Baltic shield are recognizable as distinctive fabrics or structures in the 1.7 Ga Proterozoic cratonic basement exposed at ¿sp¿. This rock mass segmented along ductile shear zones, while in the lower crust, fragmented along much the same zones as it rose into the upper crust and has been jostled mainly by repeated reactivation of the same brittle fracture zones ever since. The first strains were ductile and penetrative and shared by all the rocks of the region. Subsequent strains became increasingly localized to the boundaries of relatively unstrained blocks. Ductile gneiss zones that segmented the crust at amphibolite facies narrowed to mylonites and then faults as the rock mass passed through the ductile-brittle transition in greenschist facies at ≈1.4 Ga. Since they have been in the cool upper crust, many of the same shear zones have widened to brittle fracture ones. Fracture infills of decreasing age consist of different combinations of quartz, epidote, Fe-oxihydroxides, chlorite, prehnite, and calcite. Fragmentation (generation of new fractures) generally gave way to jostling (reactivation of preexisting fractures) in successive episodes of brittle intracratonic strain at ¿sp¿. The regional fracture pattern on all scales consists of different combinations of the same five fracture sets. By the end of Palaeozoic times, the ¿sp¿ bedrock had accumulated fracture zones with a sufficiently wide range of orientations that subsequent strains involved more jostling than fragmentation. Plate tectonic and glacial strains of Sweden anticipated in the next few million years are also likely to occur along long-established zones of weakness that are already available for study. ¿ American Geophysical Union 1993