Almost every Kunstkammer in sixteenth-century Europe contained small reptiles or plants cast from life in a variety of media. This widespread technique, which used small, recently killed animals as a pattern to create lifelike sculptures, was often prized more highly than works sculpted with the hand. An unstudied, late sixteenth-century French technical manuscript records a practitioner's experiments in casting from life, among many other subjects. This article investigates both the techniques and the significance of life-casting on the basis of this treatise, incorporating the examination of surviving sixteenth-century European life casts and the reconstruction of the manuscript's recipes and technical instructions, arguing that life-casting in the sixteenth century was viewed in part as a means to the knowledge of nature.