Qualified psychiatrists have served aboard starships since the 23rd century, although occasionally the role of chief medical officer and counselor were combined, with medical officers also having expertise in space psychology; an example of this is Doctor Leonard McCoy, of the USS Enterprise and USS Enterprise-A.
By the mid-24th century, starship and starbase crews included a dedicated counselor, who was responsible for the mental well-being of the crew and civilian staff. The position is considered vital enough that it warranted inclusion in the senior staff of the Federation flagship; in that instance at least, the ship's counselor also had a diplomatic role, advising the captain in first contact and other situations. Onboard most ships within the fleet, these diplomatic duties are delegated to a specialised diplomatic officer, though this is often at the captain's discretion.
As with the chief medical officer, the ship's counselor has the power to relieve other officers and crewmembers of duty if he or she feels that their patient is suffering from a condition that may hinder their ability to perform their duties effectively.
At the captain's discretion, the ship's counselor may be allowed to wear something other than their normal Starfleet uniform while on duty.
The Chief Counselor is considered a member of the Senior Staff. S/he is responsible for the crew in his/her department. The Chief Counselor is the Counselor with the highest rank and most experience.