First some key facts: the Sirius Passet fossil biota is the most remote, least well known and, to date, one of the least diverse of the Cambrian exceptionally preserved assemblages or Lagerstätten (Harper et al., 2019). Following its serendipitous discovery in 1984, by field geologists working for the Geological Survey of Greenland, the locality in the Buen Formation, on the edge of J. P. Koch Fjord in North Greenland has been visited by only seven collecting expeditions, most recently in 2009 and 2011 by multidisciplinary and multinational groups, led by the author when a member of staff in the Natural History Museum of Denmark, University of Copenhagen, and in 2016 and 2017 by a UK–South Korea group. The Sirius Passet Lagerstätte occurs in black mudstones deposited at the shelf–slope break on the Laurentian margin. Although deformed and metamorphosed by a Devonian tectonic event, the Ellesmerian Orogeny, the locality preserves, to a large degree, the original depositional relationships and allows an interpretation of the environmental setting of this early Cambrian ecosystem; thus it is key to understanding the environmental constraints on the Cambrian Explosion. The fossiliferous site is located in the Sirius Pass, beside J. P. Koch Fjord, Peary Land, North Greenland, at 82° 47.59ʹ N, 42° 13.54ʹ W (Figure 22.1) and an altitude of 420 m. This remote locality can only be reached by short take-off and landing aircraft that can use a rough airstrip in the valley, 2 km to the west–north-west.