The Unknown Life of Jesus Christ, originally published in 1890, is a book by Nicolas Notovitch, who was a Russian aristocrat, Cossack officer, spy, and journalist. The author claims that Jesus spent many of his missing years traversing India. The story begins in 1887, when Nicolas Notovitch went on an expedition to learn about the customs of the people of India. During his travels, he visited a Buddhist monastery where he heard about a holy man, thought to be Jesus, who visited the region 2,000 years before. The Buddhists called him "Issa" and there was an ancient document that could confirm the similarities.

As Notovitch embarked on a treacherous journey to track down the evidence, he broke his leg in an accident and found himself recuperating at a monastery that possessed a copy of the document. The chief lama showed him a scroll that described a man with an uncanny resemblance to Jesus of Nazareth and his teachings. In spite of warnings from various churches, Notovitch published his findings.

This controversial book shows where many of Jesus' beliefs come from, while at the same time showing that Jesus was already well on his way to his fundamental beliefs at a very young age.