The article examines the ‘full jurisdiction’ requirement under Article 6 ECHR and its implementation within ECtHR case law. It first analyses the theoretical foundations for ‘full jurisdiction’ which implies, in principle, a substitutive review of the merits of administrative decisions. It then focuses on the ECtHR case law, highlighting its ambivalence and inconsistencies: while the Court generally requires a substitutive review in criminal cases and in cases involving complex technical assessments, it tends to accept a less exacting standard of review in civil cases, especially when administrative discretionary choices or policy determinations are at issue. This article suggests that the ambivalence and inconsistencies within ECtHR case law can be explained in terms of the principle of separation of powers, which still underpins most legal systems of signatory states to the ECHR.