Sanctification means literally to make holy or sacred (compare Latin sanctus 'holy'). The concept of sanctification is widespread among religions, but is perhaps especially common among the various branches of the Christian religion. The core of the concept is that the special supernatural properties of holiness or sacredness commonly attributed by adherents of the religion to God or to Jesus are extended to men or things that in their ordinary state are not holy or sacred.

For example, the doctrine page http://www.sbc.net/bfm/bfm2000.asp of the Web site of the Southern Baptist Convention gives the following definition (doctrine IV.C) of sanctification:

"Sanctification is the experience, beginning in regeneration, by which the believer is set apart to God's purposes, and is enabled to progress toward moral and spiritual maturity through the presence and power of the Holy Spirit dwelling in him. Growth in grace should continue throughout the regenerate person's life."

Here, the core of the concept is expressed in the idea that the Holy Spirit "dwells within" an individual, making him holy insomuch that he experiences "grace". In most Christian denominations santification is considered a process which is ongoing throughout a Christian's life, unlike redemption.

In the Roman Catholic branch of Christianity, one who is sanctified is believed to be free from sin.

In many branches of Christianity, inanimate objects as well as men can be sanctified. A notable instance is the process of transubstantiation, which in Catholic doctrine means that the bread and wine of Communion are physically transformed into the flesh and blood (respectively) of Jesus. This act, normally carried out by priests, constitutes a kind of sanctification of the bread and wine.

The term has gathered special uses by the different denominations of Christianity. For Protestants, the concept of sanctification is tied closely to grace. For most of these churches, objects cannot be sanctified, since they lack will and spirit. Following a particular reading of the doctrine of the perseverance of the saints, "sanctified" is used as a verbal shorthand for born again. This usage is rare in churches of the Anglican communion and the Roman Catholic Church, where sanctification refers to the conveyance of blessing. Therefore, in the language of contemporary religious polemics, the term can be used as a form of identification by the evangelical churches.