532 U.S. 318 (2001)
Atwater v. City of Lago Vista is a cornerstone Fourth Amendment case that defines the scope of police authority to make custodial arrests for minor, fine-only offenses.
Does the Fourth Amendment prohibit a warrantless custodial arrest for a minor criminal offense that is punishable only by a fine when the offense is committed in the officer's presence?
When an officer has probable cause to believe that an individual has committed a criminal offense in the officer's presence—even a very minor, fine-only misdemeanor—the Fourth Amendment permits a full custodial arrest. Reasonableness does not turn on the offense's maximum punishment, a case-specific necessity showing, or the officer's subjective motives; objective probable cause suffices.
No. The Fourth Amendment does not forbid a warrantless custodial arrest for a fine-only misdemeanor committed in the officer's presence. Atwater's arrest was constitutionally reasonable.
Atwater establishes a bright-line Fourth Amendment rule authorizing custodial arrests for fine-only misdemeanors committed in an officer's presence, so long as probable cause exists. Practically, this confers broad police discretion in traffic and other minor-offense contexts and, when an arrest occurs, triggers full search-incident-to-arrest authority under Robinson. The case dovetails with Whren's objective probable cause framework and foreshadows Virginia v. Moore's holding that the Fourth Amendment's reasonableness standard is distinct from state arrest limitations. For law students, Atwater is essential for analyzing traffic-stop and misdemeanor hypos, assessing the validity of arrests and subsequent searches, and understanding the policy tradeoffs between administrability and individualized reasonableness.