In the Imperial Starfleet, the first officer was the second-in-command of a starship. The position was usually held by an officer with the rank of commander or lieutenant commander.

First officer's had the following duties and functions:

• They were the principal adviser to the captain
• They implemented the captain's orders
• They were the commander of the vessel in the event of the captain's absence, incapacitation or death
• They were to lead assault team missions when the captain presence on the ship was vital
• They had orders to assassinate the captain in the event of his failing to follow Imperial orders

Some noted first officers in Starfleet history were:

• Jonathan Archer of ISS Enterprise (NX-01)
• T'Pol of ISS Enterprise (NX-01) and later USS Defiant
• Spock of ISS Enterprise (NCC-1701)