Cross-border employees and self-employed workers are confronted with the regulations of at least two states when it comes to taxation and social security. Without delving into the specifics of national regulations, this article examines the applicable rules concerning the levy of taxes and social security contributions in the context of cross-border employment. Regulations aimed at avoiding double taxation are different from those aimed at avoiding the double payment of social security contributions. Because social security in the Member States can be financed in different ways, the levying of so-called economic double taxation is possible. This is true in particular where states use a large part of the tax revenues to finance their social security system. Cross-border workers that are required to pay taxes in these states and also pay social security contributions in another state can feel that they are paying double social security contributions. This contributes to a sense of injustice and is undesirable. The conclusion is that possible double economic contributions must be studied in a broader European context. First, the problem must be identified and then solutions formulated in order to prevent double levying.