In order to understand exorcisms, we will look at the meaning and history of them.

The word Exorcism comes from the Greek word exorkizein, which when broken down to its basic elements means ex: out and horkezen: to bind by oath and to drive off by adjuration.

One of the common misconceptions is that an exorcism is only the act of removing a Demon from a possessed person, this is actually quite false.  The practice of exorcism throughout the ages has been used to remove Demons from possessed animals, to help crops with insect plagues, & remove Demons from possessed people.

These are not the only methods of exorcism, the blessing of objects such as holy water, homes, oil, churches and sacred items. And the acts of baptism are all methods of exorcism.

Some of the first records of exorcism are from the bible, when Christ himself banished demons from afflicted people. And said that anyone could do the same.  Luke: In my name shall they cast out devils.

The Christian belief is that demons may meddle in the thoughts and activities of people as much as God permits. This is done because the faithful are able to use their free will with the grace of God to not be tempted. Demons can only tempt people they can not effect his free will. If a person permits himself to become alienated from God, and be tempted by greed, pride, fear or any other low moral standards he can easily become possessed. This is seen in the bible James 1:12, Blessed is the man who endures trial, for when he has stood the test he will receive the crown of life which God has promised to those who love him

Many different prayers of exorcism have been written throughout the years, some are very short and some are very long and require much preparation. Fasting, Prayers and Blessings are sometimes required before a exorcism.

One of the more commonly accepted versions of a prayer of exorcism is:
 

PRAYER AGAINST SATAN and THE REBELLIOUS ANGELS

PUBLISHED BY ORDER OF H.H. POPE LEO XIII

The Holy Father exhorts priests to say this prayer as often as possible, as a simple exorcism to curb the power of the devil and prevent him from doing harm. The faithful also may say it in their own name, for the same purpose, as any approved prayer Its use is recommended whenever action of the devil is suspected, causing malice in men, violent temptations and even storms and various calamities. It could be used as a solemn exorcism (an official and public ceremony, in Latin), to expel the devil. It would then be said by a priest, in the name of the Church and only with a Bishop's permission.

In the Name of the Father, and of the Son, and of the Holy Ghost. Amen.

PRAYER TO SAINT MICHAEL THE ARCHANGEL

Most glorious Prince of the Heavenly Armies, Saint Michael the Archangel, defend us in "our battle against principalities and powers, against the rulers of this world of darkness, against the spirits of wickedness in the high places" (Eph., VI,12). Come to the assistance of men whom God has created to His likeness and whom He has redeemed at a great price from the tyranny of the devil. Holy Church venerates thee as her guardian and protector; to thee, the Lord has entrusted the souls of the redeemed to be led into heaven. Pray therefore the God of Peace to crush Satan beneath our feet, that he may no longer retain men captive and do injury to the Church. Offer our prayers to the Most High, that without delay they may draw His mercy down upon us; take hold of "the dragon, the old serpent, which is the devil and Satan", bind him that he may no longer seduce the nations" (Apoc. XX,2).

EXORCISM

In the Name of Jesus Christ, our God and Lord, strengthened by the intercession of the Immaculate Virgin Mary, Mother of God, of Blessed Michael the Archangel, of the Blessed Apostles Peter and Paul and all the Saints. (and powerful in the holy authority of our ministry)*, we confidently undertake to repulse the attacks and deceits of the devil.

* Lay people omit the parenthesis above.

PSALM 67: God arises; His enemies are scattered and those who hate Him flee before Him.

As smoke is driven away, so are they driven; as wax melts before the fire, so the wicked perish at the presence of God.

V. Behold the Cross of the Lord, flee bands of enemies.

R. He has conquered, the Lion of the tribe of Juda, the offspring of David.

V. May thy mercy, Lord, descend upon us.

R. As great as our hope in Thee.

[The crosses below indicate a blessing to be given if a priest recites the Exorcism; if a lay person recites it, they indicate the Sign of the Cross to be made silently by that person.]

We drive you from us, whoever you may be, unclean spirits, all satanic powers, all infernal invaders, all wicked legions, assemblies and sects; in the Name and by the power of Our Lord Jesus Christ,+ may you be snatched away and driven from the Church of God and from the souls made to the image and likeness of God and redeemed by the Precious Blood of the Divine Lamb.  Most cunning serpent, you shall no more dare to deceive the human race, persecute the Church, torment God's elect and sift them as wheat. The Most High God commands you, He with whom, in your great insolence, you still claim to be equal; "He who wants all men to be saved and to come to the knowledge of the truth" (I Tim., II,4). God the Father commands you. God the Son commands you.  God the Holy Ghost
commands you. Christ, God's Word made flesh, commands you;  He who to save our race outdone through your envy, "humbled Himself, becoming obedient even unto death" (Phil.,II,8); He who has built His Church on the firm rock and declared that the gates of hell shall not prevail against Her, because He will dwell with Her "all days even to the end of the world" (Mat.,XXVIII,20). The sacred Sign of the Cross commands you, as does also the power of the mysteries of the Christian Faith. The glorious Mother of God, the Virgin Mary, commands you. The blood of the Martyrs and the pious intercession of all the Saints command you. 

Thus, cursed dragon, and you, diabolical legions, we adjure you by the living God,  by the true God,  by the holy God,  by the God "who so loved the world that He gave up His only Son, that every soul believing in Him might not perish but have life everlasting" (St.John,III); stop deceiving human creatures and pouring out to them the poison of eternal damnation; stop harming the Church and hindering her liberty. Begone, Satan, inventor and master of all deceit, enemy of man's salvation.
Give place to Christ in whom you have found none of your works; give place to the One, Holy, Catholic and Apostolic Church acquired by Christ at the price of His Blood. Stoop beneath the all-powerful Hand of God; tremble and flee when we invoke the Holy and terrible Name of Jesus, this Name which causes hell to tremble, this Name to which the Virtues, Powers and Dominations of heaven are humbly submissive, this Name which the Cherubim and Seraphim praise unceasingly repeating: Holy, Holy, Holy is the Lord, the God of Armies.

V. O Lord, hear my prayer.

R. And let my cry come unto Thee.

V. May the Lord be with thee.

R. And with thy spirit.

Let us pray. - God of heaven, God of earth, God of Angels, God of Archangels, God of Patriarchs, God of Prophets, God of Apostles, God of Martyrs, God of Confessors, God of Virgins, God who has power to give life after death and rest after work, because there is no other God than Thee and there can be no other, for Thou art the Creator of all things, visible and invisible, of whose reign there shall be no end, we humbly prostrate ourselves before Thy glorious Majesty and we beseech Thee to deliver us by Thy power from all the tyranny of the infernal spirits, from their snares, their lies and their furious wickedness; deign, O Lord, to grant us Thy powerful protection and to keep us safe and sound. We beseech Thee through Jesus Christ Our Lord. Amen.

From the snares of the devil, deliver us, O Lord.

That Thy Church may serve Thee in peace and liberty, we beseech Thee in peace and liberty, we beseech Thee to hear us.

That Thou may crush down all enemies of Thy Church, we beseech Thee to hear us.

(Holy water is sprinkled in the place where we my be.)

Imprimatur: +Henri, O.M.I.

Vicar Apostolic of James Bay - Aug. 15, 1967

Source: The Catholic Dispatch.

Due to the popularity of exorcisms in movies, books, and television , and other forms of media, the church has had to update its views and practices.  A recent released new information involving possession and how to tell if a possession is authentic. The new belief is that most incidents of what seem to be demonic possession can now be attributed to psychological and addiction problems, but does not account all possible possessions to this.

The Catholic church has an appointed office of exorcism to perform the service of exorcism, this office is appointed by the bishop.
 
The exorcist is expected to prepare candidates for baptisms  through prayers to strengthen him and to renounce Satan.
 
This is also the person who is called upon in the case of a possession, who by various signs the exorcist has to determine if the possessing spirit is good or evil.

In the manual of exorcism Enchiridium written by Vincentius von Berg there is a list of tests to tell if a person is possessed.
 
The indications were:
Fled at eh sight of a holy relic or at the name of Jesus.
They said anything against the Catholic faith.
The person would refuse to talk about possession to a priest.
Appeared with a dejected appearance, foul smell or noise.
Left others with a feeling of grief or desolation.
The person would be unable to retain their food, unable to digest their food and  Plagued with constant vomiting.
The person would  experience feelings of pain, such as a stabbing or knawing pain in the stomach and head.
Some people experience extreme emaciation and weakness.
The person may seem to experience physical change such as bite marks, swelling, change of skin color , Etc.
Some possessed persons were though to be able to speak in languages not spoken by them.

As we see the act of exorcism is primarily  a Catholic/Christian practice.  But as we will see later, in all corners of the world some form of exorcising Demons or evil spirits has been practiced.