This paper presents the methodology as well as the results of the joint OECD-EC project Migration-Demography Database: A monitoring system of the demographic impact of migration and mobility. The objective of the project is to evaluate the contribution of migration to past and future labour market dynamics across OECD countries. After assessing the role of migration over the last five to 10 years in shaping the occupational and educational composition of the labour force, this project looks at the potential contribution of migration to the labour force in a range of alternative scenarios. This paper presents the results from the first part of the project: it focuses on the changes that have taken place in the last 10 years and studies how migration flows have contributed to the dynamics of the labour force, in particular in comparison to other labour market entries. It also analyses the contribution of migration in specific skills categories and in specific occupations.