A counselor assigned to Starfleet vessels and installations is responsible for the mental well-being of the crew, and is a position usually held by a senior Starfleet officer with training in psychology.
By the 24th century, the counselor is considered a vital position that even warrants inclusion in the senior staff of the Federation flagship; in that instance at least, the ship's counselor also has a diplomatic role, advising the Captain in first contact and other situations.
As with the chief medical officer, the ship's counselor has the power to relieve other officers and crew members 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.
- This was the case with Deanna Troi, the ship's counselor on the USS Enterprise-D. Deanna elected to wear a uniform permanently after being told to do so by Captain Edward Jellico (TNG:"Chain of Command, Part I").
Some Starfleet officers, such as Captain Lisa Cusak and Chief Miles O'Brien, disliked the concept of a designated ship's counselor, preferring to seek advice about their problems from friends. (DS9: "The Sound of Her Voice")
- According to a early draft of "Relics" (TNG), Counselor Troi explained that the responsibility of a ship's counselor was to take care of the emotional well-being of a ship's crew and guests. Starfleet began assigning counselors to starships in the 2330s, after they realized that the pressures of extended space travel could result in psychological problems that would require professional care.
Deanna Troi trained in psycology before joining Starfleet. She served as counselor aboard the USS Enterprise-D and the USS Enterprise-E before transferring to the USS Titan with her husband, Will Riker. As well as carrying out her psychiatric and diplomatic duties, Troi served as conn officer during several emergencies and took the Bridge Officer's Test, enabling her to command the ship.
Deep Space 9 had several counselors during its time in operation, including Telnorri (DS9: "Hard Time") and Ezri Dax, who was previously an assistant counselor on the USS Destiny (DS9: "Shadows and Symbols").
The USS Voyager was not originally assigned a counselor as its mission was intended only to last a few months. Later, Neelix appointed himself morale officer, a term of his own invention, to take on the responsibilities of a counselor.