This book concentrates on federal court authority to entertain habeas corpus petitions filed by state prisoners who claim that they were convicted or sentenced in violation of their federal constitutional rights. Lower federal courts have no appellate jurisdiction to review state court judgments in criminal cases. Nevertheless, federal courts revisit state convictions and sentences indirectly when they adjudicate federal claims in habeas corpus proceedings. Federal court authority under this heading has theoretical implications for the federal system, as well as practical significance for the implementation of constitutional standards in criminal cases, particularly in capital cases.