| Name | Description | 
  
    | Ice Bore [1] | Species of worm which lives on Andoria. Ice bores tunnel through the ice by generating very high temperatures; it can be very dangerous to encounter a swarm of them unexpectedly. [1] | 
  
    | Iconian [2] | Ancient and highly advanced species now extinct [2] | 
  
    | Idanian [3] | Odo once became romantically involved with an Idanian secret operative. [3] | 
  
    | Iguana [4] | Terran reptile. [4] A member of the USS Enterprise crew was turned into an Iguana by Charlie in in 2266. [5] They where later turned back to human form by Charlies adoptive parents. | 
  
    | Ikaaran [6] | Species to be found in the Delphic Expanse in the 21st/22nd century. [6] | 
  
    | Ilari [7] | Voyager became involved in an Ilari civil war when the leader of a dissident faction transferred his personality into the body of Kes. [7] | 
  
    | Ilidarian [8] | Delta Quadrant civilisation [8] | 
  
    | Illyrian [9] | Species native to the Delphic Expanse. Archer raided an Illyrian ship in 2153 in order to steal a warp coil to repair Enterprise's drive, leaving them with a three year trip home. [9] | 
  
    | Illyrian [10] | Alpha quadrant species who specialised in adapting their bodies using genetic engineering to better fit into their surroundings, rather than altering their suroundings to suit them. [10] | 
  
    | Imaginary Species [11] | This species formed part of the delusion Hoshi Sato underwent in 2152 whilst transporting to the NX-01. In the delusion, the species was a hostile race intent on destroying the ship. [11] | 
  
    | Imhotep [12] | Delta quadrant society who took part in a regular sub-warp shuttle race [12] | 
  
    | Immunocytic Gel Worm [13] | Animal used by Dr. Phlox. [13] | 
  
    | Interphasic Organism [14] | Parasitical life forms which infested the Enterprise D [14] | 
  
    | Iothra [15] | Species which breathes hydrogen [15] | 
  
    | Iotian [16] | Highly imitative species who based their lives on earth gangsters after a visit from a federation starship. [16] | 
  
    | Ithenite [17] | Humanoid species, recognisable for their diminutive stature and copper coloured skin. A pair of Ithenite diplomats travelled to the planet Babel aboard the USS Enterprise in 2267 in order to debate the admission of Coridan to the Federation. [18] 
 The Ithenites remained Federation members in 2554, in the future shown to Captain Archer by Daniels. They were part of the war against the Sphere Builders in this time. [19]
 | 
  
    | Iyaaran [20] | Species which visited the Enterprise-D in 2370. The Iyaarans had no concepts of crime, pleasure, antagonism or love and used their visit to try and provoke some of these in the Enterprise crew. Iyaarans reproduce by post-cellular compounding, and emerge from the natal pod fully grown. There are therefore no children in their species. [20] |