This contribution presents ongoing research that sets out to assess for the first time the situation of the foreign workers, from Europe and beyond, who work in France, in various economic sectors, as a result of the operation of networks of subcontractors. It appears that neither the legal framework nor the obligations of the foreign firms employing these workers are clear, in terms either of relations with government departments or of the legal arguments that may legitimately be invoked for the settlement of disputes. Trade unions, citizens' associations, locally elected officials and civil servants alike are strikingly ill-prepared to deal with this new phenomenon of the movement of workers in Europe.