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We reconstruct seven sequential positions of the Acadian deformation front and foreland basin as these features migrated northwestward across Maine from Late Silurian to Middle Devonian 40 ^9 time. The reconstructions are based on (1) U/Pb and Arf Ar ages of pre-, syn-, and post-tectonic plutons; (2) conodont and palynomorph ages of key strata that predate or postdate the local age of deformation; and (3) interpretations of the depositional settings of these strata: far-foreland, forelandbasin, inner trench slope, and erogenic hinterland. Tight correlations between isotopically and paleontologically dated events are made possible by recent improvements in the Silurian-Devonian time scale. In early Ludlow time (-423 Ma), the deformation front must have lain near the present midline of the Fredericton basin, between the post-tectonic Pocomoonshine pluton (423 Ma) to the southeast, and the graptolitic Smalls Falls Formation of the same age, 70 km across strike to the northwest. During early Lochkovian time (-417 Ma), the deformation front was near the present midline of the Central Maine basin, as recorded by the northwestward advance of slope deposits of the Carrabassett Formation across axially-transported turbidites of the Madrid Formation. The early Emsian (406-407 Ma) deformation front lay along or near the Lobster anticlinorium; its position is bracketed between the post-tectonic Russell Mountain pluton (406 Ma) to the southeast and the brachiopod-bearing Tomhegan molasse of the same age, 50 km across strike to the northwest. At the Emsian-Eifelian boundary (-394 Ma), the deformation front was located along the Pennington-Munsungun anticlinorium, northwest of the post-tectonic Mapleton and Trout Valley Formations, but southeast of the youngest nonmarine elastics in the pretectonic Fish River Lake Formation. At the Eifelian-Givetian boundary (-387.5 Ma), the deformation front was probably somewhere near the midline of the Connecticut Valley-Gaspe basin, northwest of a belt of post-tectonic plutons in Quebec, including the 384-Ma Scotstown pluton, but southeast of three occurrences of deformed Eifelian carbonates along the basin's northwestern margin. At the Givetian-Frasnian boundary (-382.5 Ma), the deformation front was somewhere to the northwest of these Eifelian carbonate outcrops. The orogen thus migrated toward the northwest about 240 km across strike (present distance) in about 40.5 million years. Meanwhile, on the outboard (southeasterly) side of the orogen, a boundary between deformed and undeformed rocks moved toward the southeast at least 50 km, probably during the Early and (or) Middle Devonian. The migration pattern of the orogen and foreland basin suggests that during collision, a southeasterly plate that included the Acadian erogenic wedge and its Avalonian backstop overrode the Taconic-modified margin of North America. The implied minimum plate convergence rate is about 6 mm/yr. The actual rate must have been considerably faster because the base map is nonpalinspastic; a more accurate estimate w...