Federal jurisdiction (United States)
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The United States of America, being a federal country is made up of many (currently fifty) States and a central government. This central government may be known as the Union, the United States, or the Federal government. Similarly Federal jurisdiction refers to the legal scope of the Union's powers.
Legislative Branch 
One aspect of federal jurisdiction is the extent of federal legislative power. Under the Constitution, Congress has power to legislate only in the areas that are delegated to it. Under clause 17 Article I Section 8 of the Constitution however, Congress has power to "exercise exclusive Legislation in all cases whatsoever" over the federal district (Washington, D.C.) and other territory ceded to the federal government by the states, such as for military installations. Federal jurisdiction is said to exist over such territory.
Federal jurisdiction in this sense is important in criminal law because federal law, being based on a concept of enumerated powers, does not deal with crimes as comprehensively as the laws of any particular state. To fill in any potential federal gaps, Congress has enacted the Assimilative Crimes Act (18 U.S.C. § 13), which provides that any act that would have been a crime under the laws of the state in which a federal enclave is situated is also a federal crime. Since most of these enclaves are occupied by the military, military law is especially concerned with these enclaves, especially the issue of establishing who has jurisdiction and what type of jurisdiction. Specifically, in these enclaves, the federal government may have proprietary jurisdiction (only the rights of any other landowner), concurrent jurisdiction (the right to legislate concurrently with the state government), or exclusive jurisdiction over the land where an act was committed in order to establish jurisdiction over the actor. This is not necessary for courts-martial involving military members subject to the Uniform Code of Military Justice as those military members are bound by the UCMJ regardless of their location.
Judicial Branch 
The American legal system includes both state courts and federal courts. Generally, state courts hear cases involving state law, although they may also hear cases involving federal law so long as the federal law in question does not grant exclusive jurisdiction to federal courts. Federal courts may only hear cases where federal jurisdiction can be established. Specifically, the court must have both subject-matter jurisdiction over the matter of the claim and personal jurisdiction over the parties.
The Federal Courts are courts of limited jurisdiction, meaning that they can only exercise the powers that are granted to them by the Constitution and Federal Laws. For subject matter jurisdiction, the claims in the case must either: (1) raise a Federal Question (i.e., a cause of action or defense arising under the Constitution, a Federal statute, or the law of admiralty); or have diversity of parties (i.e., all of the defendants are from a different state than the Plaintiff), and have an amount in controversy that exceeds a monetary threshold (which changes from time to time, but is $75,000 as of 2011). See (28 USC 1331 and 1332)
If a Federal Court has subject matter jurisdiction over one or more of the claims in a case, it has discretion to exercise ancillary jurisdiction over other State Law claims.
The Supreme Court has "cautioned that ... Court[s] must take great care to 'resist the temptation' to express preferences about [certain types of cases] in the form of jurisdictional rules. Judges must strain to remove the influence of the merits from their jurisdictional rules. The law of jurisdiction must remain apart from the world upon which it operates".
Generally, when a case has successfully overcome the hurdles of standing, Case or Controversy and State Action, it will be heard by a trial court. The non-governmental party may raise claims or defenses relating to alleged constitutional violation(s) by the government. If the non-governmental party loses, the constitutional issue may form part of the appeal. Eventually, a petition for certiorari may be sent to the Supreme Court. If the Supreme Court grants certiorari and accepts the case, it will receive written briefs from each side (and any amici curiae or friends of the court—usually interested third parties with some expertise to bear on the subject) and schedule oral arguments. The Justices will closely question both parties. When the Court renders its decision, it will generally do so in a single majority opinion and one or more dissenting opinions. Each opinion sets forth the facts, prior decisions, and legal reasoning behind the position taken. The majority opinion constitutes binding precedent on all lower courts; when faced with very similar facts, they are bound to apply the same reasoning or face reversal of their decision by a higher court.
- A. Althouse, Standing, in Fluffy Slippers, 77 Va. L. Rev 1177, 1189 (1991) (characterizing the Supreme Court's decision in Whitmore v. Arkansas,
- 495 U.S. 149 (1990)).