This chapter discusses the main challenges in higher education comparative research, focusing on cross-national forms of comparison and presenting examples from European research. The first part stresses the importance of constructing concepts which can travel across countries. This part identifies the different vertical levels of comparison involved in higher education cross-national research, discussing how the need for exploring general patterns in higher education (e.g. globalisation and Europeanisation) is confronted with the importance of taking into account the diversity within the particular cases (e.g. institutional and individual experiences). The second part focuses on the equivalence of meaning in large-N (in particular, the Eurostudent and REFLEX datasets) and small-N studies, identifying the respective limits of the two forms of comparison. The chapter contends that comparative research in higher education could benefit from more collaboration between small-N qualitative comparativists and experts of large-N studies used in European policy-making. [For the complete volume, "Theory and Method in Higher Education Research. International Perspectives on Higher Education Research. Volume 9," see ED595152.]