This thesis deals with the subject of the Presidential system of government in the USA. In the first part, it is explained how the presidential system of government in the USA developed with the 1787 Constitution. Then, there is an explanation of each branch of government in the presidential system, which is divided into executive, legislative and judicial. The president is entrusted with the executive power, and in that part, there is an explanation of the presidential roles; what is the president responsible for and who replaces the president in case of resignation, death or incapacity of performing his duties. Congress is entrusted with legislative power. In that part, it is explained which institutions make up Congress, how are Congress members elected, the work of Congress, the relationship between the president and Congress. The courts are entrusted with the judicial power, primarily the Supreme Court, but also the lower courts. In that chapter there is a more detailed explanation of the structure, hierarchy and jurisdiction of the courts; the work of the Supreme Court; constitutional review and the significance of the Madison v. Marbury case.