II

II is the Roman numeral for 2.

II may also refer to:

Biology and medicine

Image intensifier, medical imaging equipment
Invariant chain, a polypeptide involved in the formation and transport of MHC class II protein
Optic nerve, the second cranial nerve

Ii is a Japanese surname, daimyō of Hikone:
- Ii clan, Japanese clan (Sengoku period)
- Ii Naomasa, one of four Guardians of the Tokugawa clan
- Ii Naotora, female daimyō and foster mother of Naomasa
- Ii Naoyuki, a Japanese author
II, drummer for the band Sleep Token
John Papa ʻĪʻī, a Hawaiian noble

ii (digraph), a digraph in certain romanized alphabets
ii (IRC client), short for IRC It, an Internet Relay Chat client for Unix-like operating systems
Ii, Finland, a municipality of Finland
Illegal immigrant (especially in Hong Kong and Macau vernacular)
Index Islamicus, a bibliography database of publications about Islam and the Muslim world
Internet Infidels, a discussion forum
IBC Airways (IATA code: II)
Yi language (ISO 639-1: ii)
Inanimate Insanity, an animated web series described as the "unofficial sister show" to Battle for Dream Island
Interactive Investor, an online investment platform in the United Kingdom.