Shetland officially became Christian in 997 when Sigurd, Earl of Orkney (and Shetland) met Olaf Tryggvason, the King of Norway, off the coast of Orkney.
The 'Orkneyinga Saga' says that Olaf forced Sigurd and his crew to convert to Christianity on pain of death.
There were, however, Christian priests – the “papar” – in Shetland before the Vikings came. The existence of “papa” place-names suggests that the Vikings respected the places where the priests were. The Vikings would have no objections to an additional god.
The evidence of pagan burial in Shetland is limited, perhaps to a generation but, like the evidence for early settlement, more could have been lost to the sea.
There is limited evidence for Viking Christianity, but at St Ninian’s Isle there exists an Iron-Age cist. Divided into six compartments with six babies underneath, with small stones with carved crosses at the heads, three of these were radiocarbon-dated to between the late 7th and late 10th centuries. The other three were later. All six could be from the 10th century, but the burials did not take place at the same time and could represent several generations. The combination of the Iron Age-style cists and the Christian headstones in a previously-Iron-Age graveyard, which subsequently became Christian, might suggest that these date to the cusp of conversion.
Corner posts from early Christian shrines and four later Norse carved crosses were also found at the site. But the continuity and the fact that the first excavations took place in the late 1950s, along with the lack of dating evidence, means that there is no straightforward answer to what was evidence of Pictish and what was evidence of Viking Christianity at St Ninain's Isle. (The site is best known for the collection of Pictish silver found on the site in 1958.)
Later, most head farms had their own chapel. In Unst there are examples of, possibly, 25 chapels.