The Helvetic nappes of Switzerland comprise a continuous zone of very low-grade metamorphism of up to 15 km width. In general, metamorphic grade increases within a single tectonic unit from the external part towards the internal part and increases within the nappe stack from top to bottom. However, an inverted metamorphic pattern is observed in several places. Physical conditions attending very low-grade metamorphism (=anchizone) of the Helvetic nappes correspond to a temperature range of c. 240-300 °C at pressures of c. 2-3 kbar. This Tertiary metamorphic evolution was diachronous and presumably occurred between c. 35 and 15 Ma. The Aar and Gotthard basement massifs were affected by greenschist facies metamorphism during Tertiary time. Within the Aar massif, with increasing Alpine metamorphic grade, the first appearance of green biotite, the disappearance of stilpnomelane and the microcline/sanidine transformation isograd have been mapped in metagranitoids. The oligoclase zone boundary in granitic gneisses is located in the middle of the Gotthard 'massif'. Physical conditions attending Alpine greenschist facies metamorphism of the two massifs are best constrained by fluid inclusion data from fissure quartz. For the Grimsel area, southern Aar massif, 450 °C / 4.4 kbar are indicated by the earliest fluid inclusion population. The Penninic Prealps cover nappes contain several tectonic units showing very low-grade metamorphism including the Gets nappe in the Chablais of France, the Prealpes Medianes nappe and the Niesen nappe, in the Prealpes Romandes of Switzerland. The Lepontine area of amphibolite facies grade shows a rather simple P-T distribution pattern. Temperature increases from 500 to 550 °C at the limit of amphibolite grade metamorphism in the north and west, to c. 675 °C towards the south at the Insubric line. Maximum recorded pressures of c. 7 kbar are in a central region c. 20 km north of the Insubric line, and decrease both to the north (5.5 kbar) and south (4.5 kbar). The timing of the climax of this metamorphism remains poorly known, but deeply-buried rocks reached their peak presumably between 27 and 33 Ma. High-pressure relics are preserved in the Adula-Cima Lunga nappe with inferred P-T conditions of 15-50 kbar / 600-1100 °C. In the Cima Lunga unit this very high-pressure metamorphism reached peak temperature conditions at c. 35 Ma. In the Simplon area the effects of the Tertiary Alpine metamorphism are best documented in calcareous schists (Bundnerschiefer). Along a cross-section between Brig (middle greenschist facies) and Crevola (middle amphibolite facies), the following mineral zone boundaries and isograds could be mapped with increasing grade: first appearance of biotite + calcite, garnet and Ca-amphibole, respectively; paragonite + calcite + quartz-out isograd, margarite + calcite + quartz-out isograd, scapolite-in zone boundary, and muscovite + calcite + quartz-out isograd. Along this cross-section, P-T data increase from 2-3 kbar / 400-420 °C to 6-8 kbar / 580-620 °C. The Penninic units east of the Lepontine area were predominantly metamorphosed under high-pressure greenschist facies conditions in early Tertiary time. However, blueschist facies relics are preserved in the NE part of the Adula nappe and rare (Fe,Mg)-carpholite is present in the Bundnerschiefer of northern Graubunden. The boundary region between Central and Eastern Alps in Graubunden shows a complicated metamorphic pattern of subgreenschist to lower greenschist facies conditions. This pattern is mainly controlled by the burial depth in the nappe pile and the presence of different phases of metamorphism, i.e. an oceanic metamorphism of Jurassic age and two phases of orogenic metamorphism of Upper Cretaceous and Tertiary age, respectively. In the Bergell area, orogenic metamorphism in the Gruf complex is documented by a P-T-t path culminating under granulite facies conditions (> 800 °C / 10 kbar). In the adjacent Chiavenna ophiolite, a sequence of closely spaced isograds indicates a metamorphic field gradient of 40-50  C/km, attributed to the rapid exhumation of the high-grade Gruf complex. At the eastern margin of the Bergell pluton, contact metamorphism is well documented by four isograds in serpentinites and two isograds in metapelites.