John Climacus (ca.579 - 649), also known as John of the Ladder, John Scholasticus and John Sinaites, was a seventh century Christian monk at the monastery on Mount Sinai. He is revered as a saint by both the Roman Catholic and Eastern Orthodox churches.

He came to the monastery and became a novice when he was about 16 years old, and when he died in 649 he was the monastery's abbot. He wrote a number of instructive books, the most famous of which is The Ladder of Divine Ascent or Ladder of Paradise. (It is because of this book that John is known as "Climacus", which means "of the ladder".) It describes how to raise one's soul to God, as if on a ladder. This book is one of the most widely read among Eastern Orthodox Christians, especially during the season of Great Lent which immediately precedes Easter, and on the 4th Sunday of Great Lent he is especially commemorated. The book discusses monastic virtues and vices and holds dispassionateness (apatheia) as the ultimate contemplative and mystical good in a Christian. There are thirty steps of the ladder, which correspond with the age of Jesus at His baptism and the beginning of ministry.

An icon known by the same title depicts several people climbing a ladder; at the top is Jesus, prepared to receive the climbers into Heaven. Also shown are angels helping the climbers, and demons attempting to shoot with arrows or drag down the climbers, no matter how high up the ladder they may be. Most versions of the icon show at least one person falling.

His feast day in the Roman Catholic Church is March 30th. In the eastern church, his feast day is the fourth sunday in lent. John Climactus was also known as "Scholasticus," but he is not to be confused with St. John Scholasticus, patriarch of Constantinople.