RI (disambiguation)

RI may refer to any of the following:
*Republik Indonesia
*Rhode Island ((United States postal abbreviations))
*Aquidneck Island (sometimes called Rhode Island, not to be confused with the state)
* The Rock Island railroad reporting mark RI
* Mandala Airlines (IATA airline designator)
* Raffles Institution, a prestigious school in Singapore
* Reference Implementation (computing), a software package
* Referential integrity, a concept in computer databases
* Refractive index
* Refugees International, an international humanitarian organization
* Rehabilitation International, an international disability rights organization
* The Royal Institution of Great Britain
* Ring Indicator, a signal in the RS232 serial communications standard
* Repubblica Italiana

Ri may refer to any of the following:
* A traditional unit of length in both Korea (리, ri) and Japan (里, ri) based upon the Tang Dynasty Chinese li (里, lǐ or 市里, shì lǐ)
* Ri (kana), a Romanization of the Japanese kana り and リ
* An "augmented second" in Solfege
* The commonly used and known representation of the second Swara — "Rishabam" (Carnatic) or "Rishab" (Hindustani classical music) in the Indian Classical Music form
* Riism, a neologism used as a gender-neutral pronoun in Esperanto
* Ri, Orne, a commune of the Orne "département", in France
* Rí, the ancient Gaelic word meaning King
*Isaac ben Samuel, known as the "Ri", a 12th-century French tosafist and Biblical commentator