I1

I1 or I-1 may refer to :
* I-1 (kickboxing), an
* GS&WR Class I1, a Great Southern and Western Railway
* Haplogroup I1 (Y-DNA), a human Y-chromosome haplogroup occurring at greatest frequency in Scandinavia
* Japanese submarine I-1, a 1926 Imperial Japanese Navy J1 type submarine
* LB&SCR I1 class, a 1906 British class of 4-4-2 steam tank locomotives
* Polikarpov I-1, a 1923 Soviet monoplane fighter