The Clandestine Service is the unofficial name for the United States Central Intelligence Agency's Directorate of Operations, which operates covertly in foreign countries. Clandestine Service officers are what most people mean when they think of a "CIA agent". Agents, however, are the sources recruited by the Clandestine Service officers. The CIA Seal The Central Intelligence Agency (CIA) is an American intelligence agency, responsible for obtaining and analyzing information about foreign governments, corporations, and individuals, and reporting such information to the various branches of the U.S. Government. ...

The Clandestine Service consists of three different types of officers:

1. Collection Management Officers - they are the connection between the Operations Officer in the field and the US foreign policy community, both in the United States and abroad. They guide the collection of intelligence and direct the dissemination of that intelligence. Managing the collection effort requires contact with US policymakers to determine what they need to know, and then communicating those requirements to the Operations Officers in the field for collection. They must understand operations and local operating environments, as well as maintain substantive knowledge about the countries and issues against which the Agency is collecting information.

2. Staff Operations Officers - These officers provide the various forms of fast-paced operational research and case management support needed by their colleagues overseas. They develop substantive expertise on their assigned area in order to enhance their interaction with field-based officers, and provide advice and counsel on events in the field. This track requires officers who can work quickly to establish contacts throughout the entire Agency to meet field requirements.

3. Operations Officers - These officers are also known as "Case Officers" and are responsible for the actual recruitment of sources (also known as agents) or collecting intelligence themselves. They work undercover, both diplomatic and non-official. The summary of this job, found on the CIA website, is as such:

For the extraordinary individual who wants more than a job, this is a way of life that will challenge the deepest resources of your intelligence, self-reliance and responsibility. It demands an adventurous spirit, a forceful personality, superior intellectual ability, toughness of mind and the highest degree of integrity. It takes special skills and professional discipline to produce results and to deal with fast-moving, ambiguous and unstructured situations that will test your resourcefulness to the utmost. The Clandestine Service is the vital human element of intelligence collection - on the cutting edge of American intelligence. This is an elite corps that gathers the vital information needed by our policymakers to make critical foreign policy decisions. The Central Intelligence Agency's Clandestine Service Trainee Program (CST) is the gateway to a unique overseas experience.

(found on http://www.cia.gov/employment/jobs/core_collector.html)