This chapter discusses the main elements, merits, and limitations of ’pure’ single case studies and comparative studies of a small number of cases. The argument is illustrated with the examples of a case study and a comparative study. The former focuses on administrative law applicable to hazardous industrial sites in France; the latter explores the same topic but sets the case of France against that of the United Kingdom. Both studies provide a powerful counterpoint to a number of assumptions underpinning the administrative law dispositions involved. They also provide a level of detail on the dynamics of the law in practice that other methodologies would easily miss. Furthermore, the case study approach enables drawing numerous additional hypotheses that could be tested in future research. The case study method’s limits include the risk of emphasizing theoretically interesting patterns that may be only marginally representative of practices.