This document presents a complete constitutional framework for a future human society on Mars. The Charter of the United Martian States is a confederative instrument designed for a small, dispersed, high-risk frontier environment in which sovereign city-states voluntarily cooperate under strict limits on central power. It is grounded in the Treaty on Principles Governing the Activities of States in the Exploration and Use of Outer Space (1967), the Universal Declaration of Human Rights (1948), and the historical lessons of Earth’s confederations and federations. The Charter deliberately rejects a unitary planetary state or a strong federal model in favor of: Absolute city-state autonomy in internal governance, labor-capital relations, and local resource management Unrestricted right of secession Minimal Union powers, strictly enumerated and subject to immediate judicial review A defensive, humanitarian Martian Space Guard capped at 0.2 % of population Direct democracy at the Union level (initiative, referendum, recall of the Consul) as a normative model Seven equally authentic languages (English, Latin, Russian, French, Spanish, Arabic, Chinese) with an open clause for future additions A high amendment threshold (three-fourths popular vote) with an unamendable core protecting secession, autonomy, rights, and the Guard cap The Martian Federalist is a series of twelve initial essays that explain the reasoning behind each major article and section. Written in the tradition of the original Federalist Papers, these essays defend the confederative choice, the minimal central structure, and the safeguards against tyranny and centralization. They are addressed not only to the first Martians who must ratify the Charter, but to every future generation that will inherit and perhaps amend it. This work is offered to the space-law community, to future settlers, and to anyone who believes that Mars should not repeat Earth’s mistakes of empire and coercion. It is a proposal — not a finished imposition — and invites comment, criticism, and improvement. The experiment begins with ratification. May it proceed in peace, reason, and mutual respect.