The Engadine Line is an over 50-kilometre (30 mi) long strike-slip fault in the Swiss canton of Graubünden, which extends into Italy and Austria. It runs along the Engadine Valley (which formed on the fault) and the Bregaglia Valley and offsets Austroalpine and Penninic units in a sinistral direction. The western end of the fault appears to peter out into ductile deformation in the Bregaglia Valley or continues as the Gruf Line to the southwest; the eastern end is buried by the Ötztal tectonic block and may continue as the "Inntal fault", "Isar fault" or "Loisach fault".

Total offset along the Engadine Line is about 4–20 kilometres (2–12 mi), decreasing southwest. It began in the Oligocene, but there is evidence of recent neotectonic activity, which resulted in the collapse of the Maloja Pass area at the beginning of the Holocene. Seismic activity occurs along the Engadine Line, and springs and carbon dioxide exhalations in the Engadine are linked to the fault.

The Engadine Line is an over 50 kilometres (30 mi) long northeast-trending fault in southeastern Switzerland. It was originally discovered in 1896 and named "Engadiner Spalte". It is a steeply dipping left-lateral strike-slip fault that cuts to a depth of 10 kilometres (6 mi). The total slip on the Engadine Line decreases from 20 kilometres (12 mi) in the Lower Engadine to 3–6 kilometres (2–4 mi) in the Upper Engadine and 1–2 kilometres (0.6–1.2 mi) at Sils, Maloja. The towns of Bever, Maloja, Nauders, S-chanf, Samedan, Sils, St. Moritz, Vicosoprano and Zernez are located along the Engadine Line, as is the Albigna Dam.

The fault trace is generally not recognizable on the surface, as it is buried beneath alluvium; the only outcrops are found at Maloja and at Stragliavita close to Zernez. Parts of the Engadine Line were already recognized by 1914, but it was only in 1977 that they were identified as belonging to a single fault zone, reportedly after a suggestion by a Chinese geologist. Sometimes the names "Nassereith-Silz fault" and "Scuols-Vils fault" are used for the Engadine Line, which was originally also known as Engadiner Spalte.

The Engadine Line deforms the Austroalpine and Penninic nappes and also appears in magnetic anomaly maps. It is responsible for the geologic differences between Graubünden north and south of the Engadine. The Engadine Line is sometimes considered to be a branch of the Periadriatic Fault System. The movement on the Engadine Line is part of a larger tectonic process in the Alps, whereby the mountain range is compressed in north-south direction and is thus squeezed upwards and eastwards. Of the numerous fault zones in the Eastern Alps, the Engadine Line and its northeastern extensions are the longest.

Evidence for a vertical component in fault motion and its interpretation is conflicting; the block southeast of the fault has a down-to-the-east component with normal slip in the northeastern sector of the Engadine Line that may be part of east-west extension in the Alps, while the sector in the Bregaglia Valley features an uplifting northwestern block with reverse slip that may be a recent change in fault motion. Vertical offset on the Engadine Line appears to have opposite direction east and west of Samedan–St. Moritz and has been interpreted as a rotational movement of tectonic blocks. The Churer uplift influenced the western side of the Engadine Line and generated eastward tilting.

In the Lower Engadine, the Engadine Line delimits the Silvretta covers and the Engadine Window from the Ötztal Alps block, which appears to bury the Engadine Line in part. The movement along the Engadine Line may have generated the Engadine Window by exposing Penninic rock units. The Schlining Thrust, which separates the Austroalpine Ötztal unit in the east from the Sesvenna-Campo-Silvretta units in the west, joins the Engadine Line in Austria. On its eastern end the Engadine Line may reach into the Northern Calcareous Alps and can be traced as far as the town of Imst in Austria; it may reach as far as Innsbruck. The Inntal fault is probably the northeastern continuation of the Engadine Line and has a maximum offset of 48 kilometres (30 mi), reaching the Molasse basin. The Loisach and the Isar faults are other candidate prolongations of the Engadine Line; alternatively, the former has been interpreted as a parallel fault that splits up in the Wetterstein Mountains. Later movements in the Ötztal Alps area may have overprinted the trace of the Engadine Line there. It is conjugated with dextral strike-slip faults in the Northern Calcareous Alps.

The Inn River valley formed along the Engadine Line. There, the fault runs e.g between the villages La Punt and St. Moritz. In the Samedan area, geologic research has found evidence of releasing bends and restraining bends associated with Miocene movement along the Engadine Line, as well as of normal faults linked to the Engadine Line. Offsets in road cuts at Seraplana have been associated with the fault. At Zernez the river departs the Engadine Line before returning at Scuol. The Engadine Line might form the northwestern border of the Scarl-Campo rock units. The combined effects of glacial erosion and slip along the Engadine Line generated the Lej da Segl, Lej da Silvaplauna, Lej da Champfèr and Lej da San Murezzan lakes which are traversed by the Inn River. The fault cuts across the Isola delta of Lake Sils.