The lower Penninic Simano Nappe consists of several metagrantitoids of Caledonian and Variscan age. Pre–Triassic paragneisses and –schists form the cover of these metagranites. Mafic layers and lenses are commonly observed and frequently found at the orthogneiss– paragneiss interface. Ultramafic rocks are rare and evidence for an early high–pressure event is not documented. The effects of three deformation phases can be distinguished in the northwestern Simano Nappe. The first phase D1 is associated with tight to isoclinal folds and is observed only in a few outcrops. This first phase is responsible for the formation of the Alpine nappe stack. The P–T conditions for this phase reached pressures of 9–11 kbar at circa 500 °C. These conditions are deduced by the mineral composition of chloritoid and paragonite inclusions in garnet. The stable mineral assemblage of Al–rich metapelites during this phase was Chl + Ctd + Pg + Zs ± Ky. The second deformation phase D2 produced the dominant deformation fabric in the Central Alps as observed today. Older structures were almost completely obliterated, whereas younger structures are generally much more weakly developed. D2 structures are therefore well preserved with the regional S2 foliation axial plane parallel to large–scale flat– lying isoclinal folds. During D2, garnet and staurolite grew in metapelites of suitable composition through decompression from 9–11 kbar to approximately 7–8 kbar while the temperature was still increasing to 600–650 °C. The stable mineral assemblage during this phase was Chl + St + Pg + Gt ± Ky. The third phase D3 folds are characteristically upright and oblique to the trend of earlier structures. The interference between D2 and D3 produces a very characteristic undulation of the main foliation S2, which is observed on all scales in the northwestern Simano Nappe. The peak of metamorphism was reached between D2 and D3. The prevailing metamorphic conditions during D3 are estimated at 6–7 kbar and 600–650 °C. The stable mineral assemblage during D3 was Bt + Ms + Gt + St + Ky. The structural observations are consistent with earlier studies in the region (Keller, 1968; Grond et al., 1995; Grujic and Mancktelow, 1996). Recent petrologic data from Grandjean (2001), obtained from garnet– amphibolites within the Simano Nappe, deduced pressures of up to 12 kbar. Compared to these data, the deduced P–T conditions of the present study are consistent estimates. The relationships of the adjacent Maggia Nappe and Leventina Gneisses to the Simano Nappe were still unclear at the start of this study. These boundaries were investigated in some detail. The structural study of the northern part of the Simano–Maggia boundary established that the Pertusio zone can be interpreted as the synformal southern continuation of the D2 Mogno synform. This result suggests, that the large–scale D3 Campo Tencia synform steepened the existing D2 structures in Valle Maggia. The consequence of these findings is that the Simano and Maggia Nappes actually represent parts of the same tectonostratigraphic unit, folded around this major D2 synform. The Maggia Nappe is therefore not in a synformal position as postulated by previous studies (e.g. Steck, 1998). The structural investigation of the Leventina–Simano boundary confirmed many of the quartzite locations mapped previously at this boundary. The lack of associated Mesozoic metasediments, however, does not allow these quartzites to be interpreted as nappe separators with any certainty as postulated by earlier studies (e.g. Bossard in Niggli et al., 1936). Furthermore, this work revealed a series of outcrops, particularly in the uppermost part of the