The National Instant Criminal Background Check System (NICS) is a system used in the United States to determine if a person is eligible to purchase firearms. Established in 1998, it allows licensed gun dealers to quickly check an individual's criminal history and other relevant information before completing a sale. NICS is managed by the Federal Bureau of Investigation (FBI) and relies on data from various sources, including state and local law enforcement agencies. The system helps prevent individuals with criminal records, mental health issues, or other disqualifying factors from obtaining firearms legally.