In the last few decades, there has been a considerable effort, mainly from Western liberal States, to create and develop an internationally harmonized counter-terrorist financing regime through international treaties, soft laws and Security Council resolutions, and to diffuse this regime into domestic laws. Aimed at preventing terrorism, this regime has introduced two types of measures: financial measures which involve financial institutions in the fight against terrorism, and penal measures which rely on criminalization, freezing and confiscation tools. This thesis examines the penal measures, the notions on which these measures are based, their scope and structure, the human-rights implications arising from their implementation and their consistency with the principles of criminal law. The main idea behind the adoption of these penal measures is to prevent any terrorist activities at early stage and before they are actualized. So, the measures have been designed to target any financing activities that contribute to, or facilitate, the preparation or commission of any terrorist act, or the activities of those involved in terrorist activities even when there is a tenuous or no link between the financing acts and an actual terrorist act. But there are two challenges that this regime faces: defining what is terrorism, terrorist acts or terrorist groups, the financing of which should be tackled, and whether and how far criminal law should be justifiably expanded to criminalize financing of terrorism or confiscate terrorist funds when there is no connection between acts of financing or funds and actual terrorist acts. This thesis illustrates how the lack of consensus on the definition, scope and elements of terrorism (terrorist acts, terrorist groups) has resulted in the adoption of different definitions of terrorism in contradiction with the principle of legality. This also raises doubts as to the effectiveness of the regime in terms of the enforcement of a harmonized counter-terrorist financing measures (although their effectiveness is not discussed here). The thesis argues that the expansion of the reach of criminal law to suppress activities which are not clearly and reasonably closely connected to the commission or preparation of terrorist activities is vague and unjustifiable in terms of the rule of law (especially values of legal certainty) and principles of the criminal law of Anglo-American States which have played a significant role in adoption and development of the regime. The implementation of these measures is in gross violation of some of the basic human rights and values that these States have been promoting.