美国是一个拥有50个州的联邦制国家，联邦政府所在地为哥伦比亚特区。《宪法》确立了国家政府的结构，规定了其权力和活动范围，并且划定了国家政府和各州政府之间的关系。在国家政府和州（地方）政府之间实行分权。州内建县、镇、市和乡各级，各级均设有选任政府。
美国的政府权力和职能由三个政府分支机构担当：立法机关、司法机关和行政机关。《宪法》第1条规定了立法机关并赋予了美国国会的立法权。有关总统的行政权力的规定在第2条。第3条将司法权交给了最高法院和各次级法院，由国会视必要予以确立。在这种“分权”制度下，每个机关独立于其他机关行使权力，但三者之间存在内在的“制衡”，可以避免权力的集中，保护公民的权利和自由。例如，总统有权否决由国会通过的法令，可以为联邦司法提名任职人选；最高法院有权宣布国会颁布的法律或总统采取的行动不符合宪法规定；而国会则可以弹劾总统和联邦司法和法官。
American National Government: An Overview (CRS Report) (PDF 38.1 KB)
Learn About the United States: Quick Civics Lessons (U.S. Citizenship and Immigration Services) (PDF 1.21 MB)
Our American Government (U.S. Congress) (PDF 349 KB)
Outline of U.S. Government (published by Bureau of International Information Programs, U.S. Department of State) (PDF 469 KB)
U.S. Government Manual (official handbook of the U.S. Federal Government)

美国宪法是世界上历史最久的宪法。起草者在宪法中订立了一项条款，允许在政治、社会或经济条件需要时对宪法进行修订。
美国宪法自出台至今，已经过27次修订。前10条修正案统称《人权法案》，保证个人的权利和自由。
宪法将政府权力分为三个分支–行政分支由总统领导；立法分支包括国会两院（参议院和众议院）；司法部门由最高法院领导。宪法通过制衡制度来限制各分支的作用，以防任何一个分支获得不当权力。
The Constitution of the United States
About America: The Constitution of the United States of America with Explanatory Notes (PDF 1.94 MB)
Bill of Rights
Constitutional Amendments Not Ratified
Constitutionalism and Emerging Democracies (Electronic Journal, Bureau of International Information Programs, U.S. Department of State) (PDF 260 KB)
Rights of the People: Individual Freedom and the Bill of Rights (published by Bureau of International Information Programs, U.S. Department of State) (PDF 748 KB)

总统是美国的首席统领，总统和副总统一起每四年选举一次。从1951年的宪法修正案起，每位总统只能连任两届。
总统的权力巨大，但并非是无限的。作为国家首席政策制定者，总统向国会提出立法提议，并有权否决国会通过的任何议案。 总统也是武装部队总司令。
政府的行政分支负责执行国家的法律。 副总统、各部长（内阁成员），以及各独立机构负责人在其中发挥协助作用。与总统的权力不同，这些人的责任在宪法中没有进行界定，但每个人都其有特定的权力和职能。
作为美国第45任总统，唐纳德·特朗普将统领行政分支，包括14个部、总统行政办公室，以及诸多其它独立机构。
联邦法律的日常执行和管理由不同的执行部门负责，这些部门由国会建立，负责处理国家和国际事务的各个具体领域。
各部部长由总统选出，经参议院确认，形成一个顾问委员会，即总统内阁。
Online Reading
The Executive Branch: Powers of the Presidency (Chapter 2, Outline of U.S. Government, Bureau of International Information Programs, U.S. Department of State) (PDF 76 KB)
The Papers of the Presidents of the United States (The Avalon Project at Yale Law School)

司法分支由美国最高法院领导。最高法院是唯一由宪法专门设立的法院。此外，国会还建立了13个联邦上诉法院和95个联邦区法院。总统有权在法官职位出现空缺时任命联邦法官，包括最高法院大法官。最高法院在华盛顿特区办公，其它联邦法院遍布美国各城市。
联邦法院受理与宪法、联邦法律和条约相关的案件、海事案件、涉及外国公民和政府的案件，以及联邦政府本身为当事一方的案件。除极少数例外之外，最高法院受理的都是来自下一级法院的上诉案件，其中大多数涉及对行政分支的行动以及国会或州通过的法律进行解释并判断该行动和法律是否合宪。
The Supreme Court of the United States: Highest Court in the Land (Electronic Journal, Bureau of International Information Programs, U.S. Department of State) (PDF 771 KB)
Access to the Courts: Equal Justice for All (Electronic Journal, Bureau of International Information Programs, U.S. Department of State) (PDF 246 KB)
The Changing Face of U.S. Courts (Electronic Journal, Bureau of International Information Programs, U.S. Department of State) (PDF 242 KB)
Criminal Justice in the U.S. (Electronic Journal, Bureau of International Information Programs, U.S. Department of State) (PDF 658 KB)
How U.S. Courts Work (Electronic Journal, Bureau of International Information Programs, U.S. Department of State) (PDF 709 KB)
Outline of the U.S. Legal System (published by Bureau of International Information Programs, U.S. Department of State) (PDF 5.35 MB)
Understanding the Federal Courts (The U.S. Courts) (PDF 1.29 MB)

立法分支，即国会，由50个州每州选出代表组成。宪法设立了一个两院制的机制，即美国国会，来负责国家收入和预算并起草法律。普遍认为国会通过掌管“钱袋子”来影响美国的政策。国会是美国政府中唯一可以制定联邦法律、宣布战争并使对外条约生效的分支。
众议员每两年选举一次。每位众议员代表其所在州的一个区。区的数量由每十年进行一次的普查确定。参议员每六年选举一次，分期分批进行，因此每两年都会有三分之一的参议院席位进行选举。宪法规定副总统为参议院议长。副总统只有在表决平局时才有投票权。
在副总统缺席时，参议院会选择一位临时议长。众议院自己选择自己的统领官员，即众议院议长。众议院议长和参议院临时议长均来自两院占多数席位的党派。
一部法案要想成为法律，必须先在参众两院都获得通过。无论是参众两院哪一方提出的法案，都要先在本方由一个或多个委员会进行审议、修订，并进行投票，若投票通过则由本方进行全体讨论。若通过，则送至另一方进行审议。一旦参众两院都对同一份法案的同一版本投票通过，该法案便会提请总统批准。
Online Reading
The Congressional Appropriations Process: An Introduction (CRS Report) (PDF 177 KB)
The Committee System in the U.S. Congress (CRS Report) (PDF 36 KB)
House and Senate Rules of Procedure: A Comparison (CRS Report) (PDF 118 KB)
How Our Laws are Made (United States House of Representatives)
The Legislative Branch (Chapter 4, Outline of U.S. Government, Bureau of International Information Programs, U.S. Department of State) (PDF 61 KB)
Senate Legislative Process (U.S. Senate) (PDF 133 KB)

州政府和联邦政府的组织形式相同，也是行政、立法和司法分支三权分立。一般来讲，完全属于一州境内的事务由州政府负责。这些事务包括内部沟通；产权、产业、商业和公共设施相关法规；州刑事法典，以及本州的工作环境。
在此背景下，联邦政府要求州政府不得颁布违反或触犯宪法或美国的法律和条约的法律。州和联邦管辖权有很多重叠之处。在卫生、教育、福利、交通，以及住房和城市发展领域，联邦政府已经承担愈发宽泛的职责。如今这些领域的项目往往以两级政府合作的形式开展。
美国人口普查局（隶属商务部）已经确定全国至少有78218家地方政府机关，包括市、县、镇、校区和特别区政府。
美国超过四分之三的公民住在镇、大城市及市郊。城市直接服务于居民的需要，提供从警务和消防到环境卫生准则、卫生法规、教育、公共交通和住房的一切服务。与州和联邦机构的合作都至关重要。
县隶属于州，通常包括两个或更多的县，以及几个村-但也有例外。有一个委员会负责收税、借款和拨款、制定县雇员薪酬水平、监督选举、修建和维护高速路桥，并管理国家、州和县福利项目。
Online Reading
A Country of Many Governments (Chapter 7, Outline of U.S. Government, Bureau of International Information Programs, U.S. Department of State) (PDF 70 KB)
State and Local Government: Adapting to Change (Electronic Journal, Bureau of International Information Programs, U.S. Department of State) (PDF 188 KB)

The United States is a federal union of 50 states, with the District of Columbia as the seat of the federal government. The Constitution outlines the structure of the national government and specifies its powers and activities, and defines the relationship between the national government and individual state governments. Power is shared between the national and state (local) governments. Within each state are counties, townships, cities and villages, each of which has its own elective government.
Governmental power and functions in the United States rest in three branches of government: the legislative, judicial, and executive. Article 1 of the Constitution defines the legislative branch and vests power to legislate in the Congress of the United States. The executive powers of the President are defined in Article 2. Article 3 places judicial power in the hands of one Supreme Court and inferior courts as Congress sees necessary to establish. In this system of a “separation of powers” each branch operates independently of the others, however, there are built in “checks and balances” to prevent a concentration of power in any one branch and to protect the rights and liberties of citizens. For example, the President can veto bills approved by Congress and the President nominates individuals to serve in the Federal judiciary; the Supreme Court can declare a law enacted by Congress or an action by the President unconstitutional; and Congress can impeach the President and Federal court justices and judges.
The American Constitution is the oldest written constitution in force in the world. The authors of the Constitution built in a provision for amending the document when political, social or economic conditions demanded it.
Twenty-seven amendments have been passed since ratification. The first 10 amendments to the Constitution, called the Bill of Rights, assure individual rights and freedoms.
The Constitution divides the powers of the government into three branches – the Executive, headed by the President; the Legislative, which includes both houses of Congress (the Senate and the House of Representatives); and the Judicial, which is headed by the Supreme Court. The Constitution limits the role of each branch, through a system of checks and balances, to prevent any one branch from gaining undue power.
The chief executive of the United States is the president, who together with the vice-president is elected to a four year term. As a result of a 1951 constitutional amendment, a president may be elected to only two terms.
The president’s powers are formidable but not unlimited. As the chief formulator of national policy, the president proposes legislation to Congress and may veto any bill passed by Congress. The president is commander-in-chief of the armed forces.
The executive branch of the Government is responsible for enforcing the laws of the land. The Vice President, department heads (Cabinet members), and heads of independent agencies assist in this capacity. Unlike the powers of the President, their responsibilities are not defined in the Constitution but each has special powers and functions.
As the 45th President of the United States, Donald Trump will preside over the executive branch, which includes 14 executive departments, the Executive Office of the President and numerous other independent agencies.
The day-to-day enforcement and administration of federal law is in the hands of the various executive departments, created by Congress to deal with specific areas of national and international affairs.
The heads of the departments, chosen by the President and approved by the Senate, form a council of advisers known as the President’s Cabinet.
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The judicial branch is headed by the U.S. Supreme Court, which is the only court specifically created by the Constitution. In addition, Congress has established 13 federal courts of appeals and 95 federal district courts. The president has the authority to appoint federal judges as vacancies occur, including justices of the Supreme Court. The Supreme Court meets in Washington, D.C., and the other federal courts are located in cities throughout the United States.
The federal courts hear cases arising out of the Constitution, federal laws and treaties and maritime cases; cases involving foreign citizens or governments; and cases, in which the federal government is itself a party. With minor exceptions, cases come to the Supreme Court on appeal from lower courts. Most of these cases involve disputes over the interpretation and constitutionality of actions taken by the executive branch and of laws passed by Congress or the states.
The legislative branch – the Congress – is made up of elected representatives from each of the 50 states. The Constitution sets up a bi-cameral body known as the U.S. Congress to raise and to spend national revenue and to draft laws. It is commonly said that Congress influences American policy by exercising the “power of the purse strings.” It is the only branch of U.S. government that can make federal laws, declare war and put foreign treaties into effect.
Members of the House of Representatives are elected to two year terms. Each member represents a district in his or her home state. The number of districts is determined by the census, which is conducted every 10 years. Senators are elected to six year terms, staggered so that one third of the Senate stands for election every two years. The Constitution provides that the vice-president shall be president of the Senate. He or she has no vote, except in the case of a tie.
The Senate chooses a president pro tempore to preside when the vice-president is absent. The House of Representatives chooses its own presiding officer — the speaker of the House. The speaker and the president pro tempore are members of the political party with the largest representation in each house.
To become a law, a bill must pass both the House and the Senate. After the bill is introduced in either body, it is studied by one or more committees, amended, voted out of committee, and discussed in the chamber of the House or Senate. If passed by one body, it goes to the other for consideration. Once both bodies have passed the the same version of a bill, it goes to the president for approval.
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The state governments follow the same pattern as the federal government, with power divided among the executive, legislative and judicial branches. In general, matters which lie entirely within state borders are the concern of state governments. These include internal communications; regulations relating to property, industry, business and public utilities; the state criminal code; and working conditions within the state.
Within this context, the federal government requires that state governments not adopt laws which contradict or violate the Constitution or laws and treaties of the United States. There are many areas of overlap between state and federal jurisdictions. The federal government has assumed ever broadening responsibility in matters relating to health, education, welfare, transportation, and housing and urban development. Programs in these areas are now often developed on a cooperative basis between the two levels of government.
The U.S. Bureau of the Census (part of the Commerce Department) has identified no less than 78,218 local governmental units in the United States, including municipalities, counties, townships, school districts and special districts.
More than three-quarters of the citizens of the United States now live in towns, large cities or their suburbs. The city directly serves the needs of the people, providing everything from police and fire protection to sanitary codes, health regulations, education, public transportation and housing. Cooperation with both state and federal organizations is essential.
The county is a subdivision of the state, usually — but not always — containing two or more townships and several villages. A board of commissioners levies taxes, borrows and appropriates money, fixes the salaries of county employees, supervises elections, builds and maintains highways and bridges, and administers national, state and county welfare programs.
Online Reading