RI may refer to any of the following:

• The state of Rhode Island
• The Rock Island railroad (AAR reporting mark RI)
• Raffles Institution, a school in Singapore.
• Refractive index

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)