CIA---中央情報局 (國外事務)

             CIA=Central Intelligence Agency中央情報局


FBI----聯邦調查局 (國內事務) 

           Federal Bureau of Investigation 簡稱是FBI

FBI 的任務是調查違反聯邦犯罪法，支持法律。保護美國調查來自於外國的情報和恐怖活動，在領導階層和法律執行方面對聯邦，州，當地和國際機構提供幫助，

中央情報局(Central Intelligence Agency，簡稱中情局，英文簡稱CIA）是美國最大的情報機構，主要任務是公開和秘密地收集和分析關於國外政府、公司和個人；政治、文化、科技等方面的情報，協調其他國內情報機構的活動，並把這些情報報告到美國政府各個部門的工作。它也負責維持大量軍事設備，這些設備在冷戰期間用於推翻外國政府，例如前蘇聯，和對美國利益構成威脅的反對者，例如瓜地馬拉的雅克布·阿本斯（Arbenz）和智利的阿耶蘭德（Allende）。總部設在蘭雷。中央情報局也經常搞一些暗殺活動，暗殺敵國領導人，但很少成功。

CIA的工作範圍極為廣泛 從美國領土到國外都是CIA的職責

CIA搞偵察,偷拍,監聽,策反,暗殺,逮捕反正只要是美國政府檯面上不能做的事就由CIA

簡單的說

聯邦調查局相當於我國的法務部調查局

中央情報局與國家安全局相當於我們的國安局

http://tw.knowledge.yahoo.com/question/question?qid=1305090207055

What is the Difference Between the FBI and the CIA? 

The Federal Bureau of Investigation (FBI) and Central Intelligence Agency (CIA) are two agencies in the United States which collect and act upon information that is either related to criminal activity or affects national security. Although the two cooperate in some cases, they have different areas of focus. The FBI is primarily a law enforcement agency, collecting intelligence related to domestic security and performing crime investigation. The CIA is an international intelligence agency which is not responsible for domestic security. The primary difference between the two can be illustrated in their names: the FBI investigates crimes, and the CIA gathers intelligence.

The FBI has a much wider range of responsibilities than the CIA. In addition to addressing some domestic intelligence issues, the FBI also has offices abroad to coordinate information collection. The overseas offices of the FBI alert domestic offices to potential threats and areas of interest. The FBI may determine that action should to be taken to ensure domestic security, and will dispatch field officers as they are needed.

http://www.wisegeek.com/what-is-the-difference-between-the-fbi-and-the-cia.htm