In the United States, interactions between police and citizens fall into three general categories: consensual ("contact" or "conversation"), detention (often called a Terry stop, after Terry v. Ohio, 392 U.S. 1 (1968)), or arrest. "Stop and identify" laws pertain to detentions.
Different obligations apply to drivers of motor vehicles, who generally are required by state vehicle codes to present a driver’s license to police upon request.
At any time, police may approach a person and ask questions. The objective may simply be a friendly conversation; however, the police also may suspect involvement in a crime, but lack "specific and articulable facts" that would justify a detention or arrest, and hope to obtain these facts from the questioning. The person approached is not required to identify himself or answer any other questions, and may leave at any time. Police are not usually required to tell a person that he is free to decline to answer questions and go about his business; however, a person can usually determine whether the interaction is consensual by asking, "Am I free to go?"
A person is detained when circumstances are such that a reasonable person would believe he is not free to leave.
Police may briefly detain a person if they have reasonable suspicion that the person has committed, is committing, or is about to commit a crime. Many state laws explicitly grant this authority. In Terry v. Ohio, the U.S. Supreme Court established that police may conduct a limited search for weapons (known as a "frisk") if they reasonably suspect that the person to be detained may be armed and dangerous.
Police may question a person detained in a Terry stop, but in general, the detainee is not required to answer. However, many states have "stop and identify" laws that explicitly require a person detained under the conditions of Terry to identify himself to police, and in some cases, provide additional information.
Before Hiibel, it was unresolved whether a detainee could be arrested and prosecuted for refusing to disclose his name. Authority on this issue was split among the federal circuit courts of appeal, and the U.S. Supreme Court twice expressly refused to address the question. In Hiibel, the Court held, in a 5–4 decision, that a Nevada "stop and identify" law did not violate the United States Constitution. The Court’s opinion implied that a detainee was not required to produce written identification, but could satisfy the requirement merely by stating his name. Some "stop and identify" laws do not require that a detainee identify himself, but allow refusal to do so to be considered along with other factors in determining whether there is probable cause to arrest. In some states, providing a false name is an offense.
Do your research for your state. Know your rights.