Occupational pensions are a key part of the pension system in many EU Member States where they provide workers with social protection in retirement. Their relevance should increase given Europe’s old-age pensions crisis. However, occupational pensions are characterised by the complexity and diversity of benefit structures, financing methods and membership rules. This conceptual mosaic has led to different categorisations at national and EU level although solidarity at work and dignity in retirement remain at the heart of European pension systems. The EU’s new legal landscape supports the social vocation of the free movement of workers. Social security rights are already protected under Article 48TFEU and Coordination. This thesis argues that EU law must protect migrant workers’ occupational pension rights. Member States are clearly facing common demographic, economic, social and political challenges. Moreover, the notion of occupational pension in EU law supports its characterisation as social protection. The justification of a social rationale to the free movement of workers is based on fundamental rights, the EU’s social objectives and values as well as the requirement of ‘social protection mainstreaming’ under EU law. The second part of this thesis claims that EU law has historically failed to deliver adequate protection of migrant workers’ occupational pension rights, stemming from a longstanding regulatory gap in which the EU’s legislative process has been hamstrung by institutional constraints. Positive integration has remained limited but a recent breakthrough in secondary legislation will bring a new social protection dimension to the free movement of workers, albeit one based on minimum requirements. Negative integration has also been limited, especially in horizontal situations despite recognition of the indirect effect of Article 45TFEU. However, fundamental rights are capable of providing a tool for the interpretation of the free movement of workers to ensure a more holistic respect for their social protection.