RI may refer to any of the following:

• The state of Rhode Island
  • Aquidneck Island (sometimes called Rhode Island)
• The Rock Island railroad
• Raffles Institution, a school in Singapore.
• Refractive index
• The Royal Institution of Great Britain

Ri may refer to any of the following:

• The two-letter English word referring to an aquatic creature in Japanese mythology described as a mix between a human and a jellyfish
• The Hepburn romanisation of the Japanese character, (hiragana) り (katakana) 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.
• The neologism as a gender-neutral pronoun in Esperanto (please refer to Riism)
• The Royal Institution of Great Britain