The specific processes involved were known to involve a spell and a very horrible act. To split one's soul, one must also commit the most supreme act of evil —murder — and then encase a portion of their fractured soul into a chosen object with the spell. The detached soul fragment would always remain as it was when it was divided. For example, Tom Riddle's diary portrayed Tom Marvolo Riddle as a teenager, and the eyes inside Salazar Slytherin's Locket resembled Voldemort's eyes as they were when he looked more human.

Though a Horcrux can be made from anything (including living creatures), Lord Voldemort chose to use objects of great significance or importance. The process made the part of the soul remaining in the witch or wizard unstable. If the maker's physical body was later destroyed, he or she would live on in a non-corporeal form, although there were methods of regaining physical form. However, according to Horace Slughorn, few would want to live in such a form and death would be preferable instead.

It was stated at one point that Voldemort had already "pushed his soul to the limit" in creating his seven Horcruxes. This implied a finite number of Horcruxes any one person may create before the process became too dangerous to attempt again. Though this limit was never explicitly stated, the number seemed to be set solidly at seven intentional Horcruxes, and creating seven Horcruxes in addition to the person's own body rendered the soul unstable and liable to break off when the person whose soul it was committed murder. Dumbledore explicitly stated that Voldemort's soul had become so unstable that it finally "broke apart" when Voldemort tried to murder Harry Potter for the first time on October 31, 1981 in Godric's Hollow.