The Magnum Opus is an Alchemical term for the process of working with Prima Materia (Prima Materia is the first chemical, the primitive base, raw chaos) to make the Philsophers' Stone.

The Magnum Opus has been carried forward in New Age and neo-Hermetic movements which sometimes attached new symbolism and significance to the processes. The original process philosophy has four stages nigredo, the blackening or melanosis albedo, the whitening or leucosis citrinitas, the yellowing or xanthosis rubedo, the reddening, purpling, or iosis