The Réunion ibis or Réunion sacred ibis is an extinct species of ibis that was endemic to the volcanic island of Réunion in the Indian Ocean. The first subfossil remains were found in 1974, and the ibis was first scientifically described in 1987. Its closest relatives are the Malagasy sacred ibis, the African sacred ibis, and the straw-necked ibis. Travellers' accounts from the 17th and 18th centuries described a white bird on Réunion that flew with difficulty and preferred solitude, which was subsequently referred to as the "Réunion solitaire".

The ibis are a group of long-legged wading birds in the family Threskiornithidae that inhabit wetlands, forests and plains. "Ibis" derives from the Latin and Ancient Greek word for this group of birds. It also occurs in the scientific name of the western cattle egret mistakenly identified in 1757 as being the sacred ibis.