Which agency is responsible for national intelligence and security?

The Central Intelligence Agency (CIA) is primarily responsible for national intelligence and security, conducting global intelligence operations that inform national policy decisions. The CIA focuses on gathering information from foreign nations and non-state actors, and it works to provide analysis and insights to support national security goals.

In contrast, while other agencies play vital roles in intelligence and security, they have more specialized missions. The Defense Intelligence Agency (DIA) primarily supports military operations and defense policy, emphasizing military intelligence. The National Security Agency (NSA) focuses mainly on signals intelligence and information assurance, which is crucial for supporting communications and information security but is not as broad in scope as the CIA's mission. The Federal Bureau of Investigation (FBI) primarily handles domestic intelligence and law enforcement, focusing on criminal activities and counterintelligence within the United States.

Therefore, the CIA's broader mandate makes it the correct answer in the context of national intelligence and security.