The aim of the article is to present the possibility of conceptualising of a significant, unclear, and difficult to explain European integration phenomenon called Schengen. Presenting the ambiguous definition of Schengen and the effects of literature review, the article shows the deficit of in-depth analyses of this sphere of European integration. To overcome this problem, theories of European integration are helpful. Based on these theories, the article presents three major levels of theorising on which Schengen can be conceptualised. At each of these levels, this issue will be analysed in a different way as: a special example of European integration, a model of European territoriality and a project of border governance in Europe. Each of these approaches has its separate theoretical framework and assumptions, uses a different conceptual apparatus and formulates different research questions.