To create a horcrux, a wizard has to damage their soul. This can only be achieved by deliberately commiting a murder. This is the supreme act of evil, resulting in the sundering of their own soul. Only a true, deliberate and conscious act of murder against another person without any regret or remorse would suffice to rend the soul.

^{A wizard who wished to create a Horcrux would then use that damage to their advantage by casting a spell which would sever the damaged portion of the soul and encase it in a designated object. The object used to contain the soul fragment could be just about anything, even a living being or creature could be made into a Horcrux. However creating a Horcrux out of an inanimate object was preferable, as it decreased the chances of it being destroyed.}

As long as that object remains intact, the soul fragment inside it lives on.

The only known way to truly reunite the pieces of soul contained within a horcux was for the creator to feel genuine regret and remorse for what they had done to make them. This process is said to have been extremely painful, even potentially fatal, to any who did so.

Horcruxes were said to be essentially the opposite of a person. Where a person's container, their body, could be destroyed without any damage to their soul, the fragment of soul contained inside a Horcrux was dependent on the container for its existence. If the container was destroyed, so too would the fragment of soul within it be.

As a fragment of the maker's soul, a Horcrux seemed to retain the identity of its creator at the time of its creation. Voldemort, for instance, created a Horcrux (his diary) during what was presumably his fifth year at Hogwarts. As such, the fragment of soul contained within the Horcrux took on the appearance and mannerisms of Voldemort as he had been when he was sixteen years old.