Intermittent, widespread and often bimodal magmatism characterized the Mesoproterozoic development in both western Baltica and eastern Laurentia. Interogenic intrusions representing early episodes of post-Gothian and pre-Sveconorwegian/Grenvillian magmatism in SW Sweden, have yielded U-Pb zircon ages at 1502±2, 1503+3/-2 and 1457±6 Ma. Integration of these new ages with well-constrained U-Pb data for other 1.53-1.13 Ga interorogenic intrusions in western Baltica implies that crustal addition occurred in discrete magmatic episodes. The occurrence of temporally and petrologically similar rocks in the North Atlantic region supports models of a coherent Laurentia-Baltica supercontinent during the Mesoproterozoic. The prolonged interogenic magmatism in Baltica east of the Oslo Rift was typically manifested by mafic dyke swarms and gabbro-dolerite-granite complexes. This lithological association, absence of attendant regional deformation and lack of evidence of continental-margin processes, collectively imply an intracratonic position for this segment between 1.50 and 1.20 Ga. It further implies that some segment of Baltica west of the Oslo Rift was attached prior to 1.50 Ga. These observations also imply that large-scale rifting, now dated at 1.46 Ga in western Baltica, did not lead to full-scale crustal separation and development of a new continental margin. During the same period, the evolution in eastern Laurentia included orogenic conditions at 1.51-1.45 Ga, and continental margin events between 1.45 and 1.19 Ga. This discrepancy in tectonic settings for eastern Laurentia and the area in Baltica east of the Oslo Rift indicates fundamental geodynamic differences along the southern margin of Mesoproterozoic Laurentia-Baltica or that the lesser-known segment west of the Oslo Rift may have been close enough to the proto-margin to experience an evolution more akin to that of eastern Laurentia.