This paper is part of the joint project between the Directorate General for Migration and Home Affairs of the European Commission and the OECD’s Directorate for Employment, Labour and Social Affairs on “Review of Labour Migration Policy in Europe”. This document has been produced with the financial assistance of the European Union. The views expressed herein can in no way be taken to reflect the official opinion of the European Union. Grant: HOME/2013/EIFX/CA/002 / 30-CE-0615920/00-38 (DI130895) A previous version of this paper (DELSA/ELSA/MI(2015)5) was presented and discussed at the OECD working party on migration in June 2015. The functioning of labour markets in the European Union can benefit if third-country nationals become more mobile between EU member states. Using micro data from the EU Labour Force Survey, this paper measures their mobility and investigates whether it is raised by naturalisation or long-term resident status. While third-country nationals are overall less mobile than EU citizens, tertiary-educated persons appear equally mobile in both groups. Raising the mobility of all third-country nationals to the level of EU citizens would add at least 25 000 mobile persons. Causal effects on mobility from long-term resident status and naturalisation are identified through a difference-in-difference approach. Results suggest that long-term resident status increases the mobility of third-country nationals by 2%-6%. To avoid selection bias in the results for naturalisation, this paper draws on a natural experiment: following the accession of Central and Eastern European countries to the EU, all their citizens indiscriminately obtained the rights of EU citizens. The evidence suggests that those who were already living in other EU countries became more mobile as a result. These findings highlight that intra-EU mobility of third-country nationals depends on their rights to reside and work in other EU countries.