This essay examines the recent electoral success of the Sweden Democrats (SD) in the Swedish municipal election in 2006 and 2010. By using statistical methods it aims to explain which of three contradicting theoretical frameworks best can explain how a populist radical right party could penetrate one of the most stable party systems in the world. The theoretical approaches tested in this essay are: a demand-side, an external supply-side and an internal supply-side approach. By using theoretically anchored proxies to determine the effect of the contradicting theoretical approaches this essay concludes that the internal supply-side explanation measuring the local party organizational ability of the SD had the most substantial effect when it comes to explaining their recent electoral success in the Swedish municipalities, as opposed to a more commonly believed demand-side driven explanation.