During the first decades of the post-war era, Sweden experienced a rapid increase in labour immigration. Many of these migrants found employment in the industrial sector, where they became concentrated. This concentration varied between different industries, but was amongst the highest in the metal and engineering industries. The aim of the thesis is to explain why migrant workers were concentrated in the Swedish metal and engineering industries during the post-war period, circa 1946-67. For this aim the thesis uses case studies, one on the regional level and another at the company level, in order to investigate and differentiate between different explanations. A varied set of different direct, as well as underlying causes and circumstances have been suggested in previous research to explain this uneven distribution of migrant workers on the labour market. Different explanations arising from these perspectives have been used in prior research with some success, but they rarely confront explanations from other perspectives, thus creating different narratives driven by different circumstances, causes, processes and intentions. The ambition of this thesis has been to seek explanations for a complex and changing historical process in post-war Sweden. In order to study this, explanations from previous research have been used to find the reasons and causes behind the concentration of foreign workers in the metal and engineering industries during the post-war era. At the same time, the results of these empirical studies are used to problematize and question these established explanations. The results have led to a somewhat different picture of the circumstances and reasons that shaped the labour immigration and the distribution of foreign employees on the Swedish labour market during the post-war period. The thesis particularly stresses that the possibilities and capabilities of the employers had a significant impact on the distribution of foreign workers.