What does Sydney Bristow do for a living?
 

Sydney is a double agent — a spy working for SD-6, and an intelligence officer with the CIA working to bring down SD-6.

Initially, her involvement with SD-6 was desk work, advancing later to reconnaissance missions, dead drops, brush passes and other field work. Her father, Jack Bristow, is also tied to both agencies; an agent of long standing with the CIA, and a Senior Officer at SD-6. Most critical to their safety, SD-6 must never learn of their connection to the CIA or they will be "terminated."

Sydney came to work with the CIA through her involvement with the Los Angeles SD-6 cell, which recruited her while she was a college freshman studying Literature. Michael Vaughn was assigned as her handler; it is also clear that he has developed feelings for her.