Caesar of Heisterbach, also known as Caesarius of Heisterbach ca. 1170 - ca. 1250, was the prior of a Cistercian monastery in Heisterbach in what is now Germany.
He is best known as the compiler of a book of hagiography that contains many wondrous tales of miracles, the Dialogus magnus visionum ac miraculorum, which is a consistenly readable and entertaining, if somewhat sensationalistic and credulous, compilation of that lore. The work was often referred to by preachers seeking material for sermons in the late Middle Ages. The work was popular and was widely distributed, showing that it catered well to the tastes of the times; it was perhaps the second largest late mediaeval best-seller, second only to the Golden Legend of Jacobus de Voragine.
He is also remembered for a maxim on the rise and fall of monasteries; he wrote that discipline causes prosperity in a monastery, and prosperity undermines discipline.