The dissertation comprises complex and system comparative-legal research of Ukrainian criminal legislation and federal criminal legislation of the United States of America. The author proposes the system of grounds concerning existence of substantial methodological bases and theoretical-applied prerequisites of realization of comparative analysis of the criminal legislation of Ukraine and the USA (on the federal level) in the present conditions. The attention is accentuated on the distinctive features of American federal criminal-legal norms, characterized by exceptional international and motivating influence. The genesis and source base of the criminal legislation of Ukraine and the USA (on the federal level) are researched. The author also emphasizes the principal comparability of Ukrainian and American (on the federal level) criminal legislation despite the fact, that both countries belong to different legal families and are characterized by the distinctive system of state structure, which led to the discovery of positive and negative features, similarities and differences in the criminal legislation of the mentioned states. It is proved, that in the U.S. modern criminal legislation (on the federal level) has a relatively definitive character (while in Ukraine - an absolutely definitive character as all crimes are gathered in the Criminal Code only) as it's not only codified in title 18 "Crimes and Criminal Procedure" of the U.S. Code, but incorporated in the special normative-legal act - Federal Criminal Code and Rules (at that, some 36 titles of the U.S. Code contain norms regarding criminal responsibility for concrete offences). In the thesis it is also established, that in contrast to the U.S. Model Penal Code present American federal criminal legislation primarily influences the formation of criminal-legal policy of the States. The dissertation contains the analysis of the main conceptual apparatus used by Ukrainian and American (on the federal level) criminal legislation and presents correspondingdata of criminal statistics, court practice and achievements of criminal-legal doctrine in the mentioned countries. The thesis comprises the comparison of normative and theoretical criminal-legal approaches in Ukraine and the USA (on the federal level) concerning crime concept, classification of crimes, uncompleted crimes (previous criminal activity) and complicity in crime, corpus delicti ("actus reus" and "mens rea"), circumstances excluding criminality of act (defenses), relief from criminal responsibility. In this connection the attention is accentuated on the norms of federal criminal legislation of the USA concerning responsibility of corporations, plea agreements, rewards for information, leading to arrest or conviction of those responsible for committing crimes etc. Moreover, the researcher discovered that normative definitions of crime, guilt and its forms, types of plurality of crimes, punishment and some other categories are absent in American federal criminal legislation, which leads to their interpretation by the doctrine and court practice of the U.S. In the process of comparing provisions on punishment in the criminal legislation of Ukraine and the USA (on the federal level), the main attention was paid to the concept of punishment, its purpose and types, assignment of punishment, criminal-legal measures which are not considered as punishment (measures of security), characteristic features of juvenile criminal responsibility and punishment in both countries. In connection with absence in Ukrainian criminal legislation of norms on restitution, order of notice to victims, probation and other institutions existent in the federal criminal legislation of the USA, the author analyzes their matter. In addition, the paper contains analysis of provisions of the Guidelines Manual presented by the U.S. Sentencing Commission. According to the criminal legislation of Ukraine and the USA (on the federal level) four groups of crimes are thoroughly compared such as crimes against person, property, in the sphere of economic activity and crimes against public security. The author defines and discloses features of definite American federal crimes unknown for Ukrainian legislation (e.g., domestic violence and stalking, telemarketing fraud, animal enterprise terrorism, illegal gambling etc.) as well as researches specific groups of respective infringements, such as hate crimes, intellectual property crimes, white-collar crimes etc. It is established that some provisions of the U.S. federal criminal legislation don't have any analogues in the Criminal Code of Ukraine (e.g., crimes against Indians) and vice versa (e.g., Federal Criminal Code and Rules doesn't contain crimes against safety of production, while responsibility for military crimes is mainly envisaged for by the special law - Uniform Code of Military Justice approved on August 10, 1956). The researcher also found out that in the U.S. Federal Criminal Code and Rules the whole chapters with a number of articles of the respective titles of the U.S. Code are devotedto the issues of responsibility for espionage, torture, kidnapping, theft, fraud, extortion, embezzlement, taking or giving of bribe, piracy, tax evasion and some other offences (while the Criminal Code of Ukraine contains only separate articles devoted to every mentioned crime). Also the author defines the system of typical mistakes made by Ukrainian scientists in the process of researching U.S. federal criminal legislation and possibilities to adopt positive American experience. Significant conclusions are made and respective propositions concerning improvement of Ukrainian national criminal legislation and legal practice are formulated in the dissertation (in particular, the draft law containing 70 legislative propositions is developed).