Over the last couple of decades, Sweden and Denmark have come to symbolize opposite policy positions on immigration and integration; the former liberal, tolerant and multicultural, the latter restrictive, nationalist and assimilationist. The marked difference between two otherwise similar countries has puzzled comparative researchers and area specialists for more than two decades. In this paper, a series of well-known but seldom compared explanations are reviewed to gain a fuller and more multifaceted understanding of why Sweden and Denmark became so different. The explanations are divided into four main approaches with different foci: the electorate, the media, the political parties and national models. The paper ends with a short conclusion, highlighting what each of the explanations contributes to a fuller understanding of the difference, and a short note on the possible convergence of the countries post-2015.