Class I is a starship classification term used to describe a type of starship in relation to other starship types in similar fleets.

In the 23rd century, the Constitution-class starship was considered to be a class I heavy cruiser by the Federation Starfleet, the Saladin-class was considered to be a class I destroyer, the Hermes-class was considered to be a class I scout, the Federation-class was considered to be a class I dreadnought and the Ptolemy-class was considered to be a class I transport/tug. (TOS reference: Star Fleet Technical Manual)