Federal crimes are criminal offenses based on legislation (laws or statutes) enacted by the United States Congress and published in the United States Code (U.S.C.). Most crimes (murder, rape, assault, burglary, etc.) are prosecuted under state law (statutes) and are known as state law crimes. In contrast, crimes prosecuted under federal law are known as federal crimes.

Federal crimes generally involve a subject over which the United States Constitution gives the federal government—and more specifically, the U.S. Congress—the power or authority to legislate or make laws. This power or authority is also known as jurisdiction.

For example, the federal government (and not the states ) has the exclusive authority to print money and regulate its value. And because bank deposits are guaranteed (insured) by the federal government (FDIC) up to $250,000 per depositor, per FDIC-insured bank, and per ownership category, bank robbery is a federal crime (18 U.S.C. §2113). Examples of other federal crimes include tax evasion, wire fraud, mail fraud, immigration offenses, voting or electoral fraud, counterfeiting money, espionage (spying), and damaging or destroying mailboxes.

In Montana, as in other states, federal crimes are offenses that fall under the jurisdiction of the federal government, as established by the United States Constitution and federal legislation. These crimes are distinct from state crimes, which are prosecuted under Montana's state laws. Federal crimes typically involve matters that cross state lines or affect federal interests, such as the regulation of currency, interstate commerce, or national security. For instance, bank robbery is a federal crime because banks are federally insured by the FDIC. Other examples of federal offenses include tax evasion, wire and mail fraud, immigration violations, and espionage. These crimes are prosecuted by federal attorneys in federal courts, and the penalties are often more severe than for state crimes. It's important for individuals in Montana to understand that while they are subject to state laws, they are also subject to federal laws, which can be enforced by federal agencies such as the FBI, IRS, and ICE.