John VIII was pope from 872 to 882.

He is often considered one of the ablest pontiffs of the 9th century. He was born in Rome. Among the reforms achieved during his pontificate was a notable administrative reorganisation of the papal curia. With little help from European kings, he attempted to expel the Saracens from Italy after they had penetrated as far as Rome. He failed and was forced to pay tribute. John defended St. Methodius against his German enemies, who objected to his use of the Slavonic language in the liturgy. John later confirmed the permission to use Slavonic that had been originally granted by Pope Adrian II, John's predecessor. In 879 he recognised the reinstatement of Photius as the legitimate patriarch of Constantinople; Photius had been condemned in 869 by Pope Adrian II. In 878 John crowned Louis II, king of France. He also crowned two Holy Roman Emperors: Charles II and Charles III.

According to the legend of Pope Joan, a woman named Joan reigned as Pope under the name of John VIII earlier in the 9th century; the legend says that she was erased from the historical record when her identity was discovered. The title John VIII was later assumed by the person described above.