State and non-state terrorism poses complex challenges to international criminal law, as the absence of a comprehensive and universally binding definition, coupled with overlapping legal regimes, complicates the criminal characterization of conduct and determination of criminal responsibility. This study aims to elucidate the legal criteria for identifying terrorist acts, examine their attribution to state and non-state actors, and assess the implications of double standards for criminal accountability. Employing a descriptive-analytical method with a comparative approach, the research draws on international legal instruments, counterterrorism conventions, international humanitarian law, the Rome Statute, and international judicial jurisprudence. The findings indicate that legal characterization requires examining the material and mental elements of conduct, the nature of the target, the status of victims, and the circumstances surrounding the act, particularly the existence of armed conflict. In armed conflicts, the prohibition of acts or threats of violence primarily intended to spread terror among civilians must be distinguished from other prohibitions against attacks on civilians. Furthermore, state responsibility for internationally wrongful acts differs from the individual criminal responsibility of state officials and members of armed groups. The exercise of international criminal jurisdiction requires establishing the constituent elements of crimes falling within the competent tribunal's jurisdiction. The principle of legality also precludes substituting terrorism-related labels for proof of legally defined criminal elements. The findings further suggest that selectively applying legal criteria based on perpetrators' identities or political considerations may undermine equality before the law and consistency in criminal accountability.