The purpose of the present work is to compare the nature, the role and the structure of the bodies responsible for tax litigation in Italy and in the United States: the “Commissioni Tributarie” and the “U.S. Tax Court” (par. 1). The essay starts from a terminological clarification related to the notion of “tax justice” (par. 2) and then describes the comparative aspects of this phenomenon, adopting a classification that divides all modern Countries into three “models” of resolution of tax disputes: the “monistic” one, the “dualistic” one and, finally, the “mixed” system, that combines features of both the previous models (par. 3). Relying on an historical and constitutional approach, the paper then investigates the evolution of both the “U.S. Tax Court” (par. 4) and the “Commissioni Tributarie” (par. 5) from executive agencies into real Courts, in order to highlight – in a comparative perspective – similarities and differences between the Italian tax litigation system and the U.S. one, having regard to the crucial issues of constitutional legitimacy, separation-of-powers principles and compliance with the guarantees of “due process” (par. 6).