SEK - Svensk krona

Early Currency in Sweden
During the medieval period, Sweden used silver currency. In 1625, however, copper coins were introduced and the currency system was switched to a bimetallic standard. In 1745, Sweden suspended its copper standard, issued irredeemable banknotes, and imposed an in-convertible paper standard. Due to inflation and major economic problems, the currency depreciated and Sweden returned to the silver standard system in 1776.

From the Swedish Riksdaler to the Swedish Krona
The currency used from the 17th Century to 1873 was the Riksdaler. The system was quite complex, with subunits consisting of mark, öres, pennings, skillingars, and runstyckens. In 1855, Sweden adopted the decimal system when they introduced a new version of the Riksdaler: the Risksdaler Riksmynt. The Swedish Krona first came to existence when Sweden agreed to join the Scandinavian Monetary Union in 1873, alongside Denmark and Norway. All countries involved fixed their respective currencies against gold at par with one another to create monetary stability. This union lasted until World War I, when the countries lost their pegs to gold. Sweden kept the Krona currency after the monetary union was disbanded.

The SEK and the euro
Under the 1994 Accession Treaty, Sweden is supposed to join the Eurozone and adopt the euro. In 2003, however, a referendum was held, resulting in 56% opposition to joining. There is still much debate whether it would be in the best interest for the country to join and as such, has delayed the adoption of the euro.