The increasing importance of international assignments goes on with the internationalisation of business activities. Due to the high number of assignments companies are required to minimise the assignment costs. Taxes and charges levied on the assigned employees income often are shifted to the employer and thus are part of the assignment costs. The scope of this study is to give an overview of the relevant tax and social security regulations in selected countries over the world and compare them among each other. Furthermore, we measure the assignment costs taking account of the taxes and charges shifted from the expatriate to the employer. The study covers twenty countries in Europe, the United States, and Asia.