This chapter discusses the persistent monopoly of the grands corps in the production and mobilisation of policy analysis in the French context. Top officials have historically built their legitimacy on detention of ‘generalist’ policy knowledge, transmitted within administrative grandes écoles, and mobilised at the central level. However, the diversification of policy experts within French administration and the rise of alternative legitimate knowledge has questioned this ‘generalist model’. Two significant evolutions are the increasing influence of ‘numbers’ compared to more traditional literary or legal skills and the shift of policy expertise downstream the policy process, as top civil servants’ work has been increasingly oriented toward policy evaluation and performance measure. Their ability to master these new types of policy knowledge certainly conditions the persistence of their power over rival actors both inside and outside government, to address the growing policy expertise of consultants, private-sector experts and members of interest groups.