Mass emigration from Sweden and Norway has been studied from many points of view. There remains, nonetheless, an often confusing debate as to which factors were responsible for causing the emigration. Although less often discussed, there remains a similar lack of consensus as to which factors slowed the flow of emigrants. In Sweden we have analyzed four schools of thought regarding the determinants of the growth and decline of emigration: peasant ecology, change and response, economic, and innovation diffusion. In Norway it was possible to examine all available but the economic factors. These theories do not exhaust all the reasons that have ever been advanced as to the causes of emigration, but they do cover the primary explanations given by present day scholars.