The marriage tag has been through several revisions in an effort to be the most useful and the least polarizing. There are two specific meta posts that should be reviewed and considered first before making suggested edits:

• Proposal for tagging questions that concern marriage, both traditional and non-traditional forms

• Suggestion for a minor change to the marriage tag excerpt

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Marriage is defined differently by various Christian faiths:

• The catholic Church teaches that Marriage is the lifelong union between a man and woman with openness to children
• The orthodox Church teaching is similar to the Catholic Church makes provisions for divorce over and above the annulment process
• Most Mainline protestant Denominations and Evangelical Churches teach that marriage is a covenant between a man and a women, but allow for divorce and, in some cases, remarriage as well as limiting family size (but still believe that marriage is the foundation of the family unit)
• The lds Church recognizes marriage between a man and a woman. The LDS Church also believes in the covenant of eternal marriage, called a sealing, between a man, a woman, and God.
• Still other Christians have other practices and beliefs concerning what they consider to be marriage which may be discussed here.

Some questions on this site explore the boundaries of the term "marriage":

• The Bible seems to allow polygamy. Why doesn't the church?
• When did the prohibition of marriage for priests in the Catholic church originate?
• What does the bible say about interracial marriages?
• How do Christians in support of gay marriage interpret anti-gay Bible verses?
• Does the act of sex constitute marriage in God's eyes?

According to Genesis:

Then the LORD God said, “It is not good that the man should be alone; I will make him a helper fit for him.” Now out of the ground the LORD God had formed every beast of the field and every bird of the heavens and brought them to the man to see what he would call them. And whatever the man called every living creature, that was its name. The man gave names to all livestock and to the birds of the heavens and to every beast of the field. But for Adam there was not found a helper fit for him. So the LORD God caused a deep sleep to fall upon the man, and while he slept took one of his ribs and closed up its place with flesh. And the rib that the LORD God had taken from the man he made into a woman and brought her to the man. Then the man said,

“This at last is bone of my bones  
    and flesh of my flesh;  
she shall be called Woman,  
    because she was taken out of Man.”  

Therefore a man shall leave his father and his mother and hold fast to his wife, and they shall become one flesh. And the man and his wife were both naked and were not ashamed.

(Genesis 2:18-25 ESV)

Paul, in the New Testament, often compares the relationship between the Church and Christ to the marriage covenant:

Husbands, love your wives, as Christ loved the church and gave himself up for her, that he might sanctify her, having cleansed her by the washing of water with the word, so that he might present the church to himself in splendor, without spot or wrinkle or any such thing, that she might be holy and without blemish. In the same way husbands should love their wives as their own bodies. He who loves his wife loves himself. For no one ever hated his own flesh, but nourishes and cherishes it, just as Christ does the church, because we are members of his body. “Therefore a man shall leave his father and mother and hold fast to his wife, and the two shall become one flesh.” This mystery is profound, and I am saying that it refers to Christ and the church. However, let each one of you love his wife as himself, and let the wife see that she respects her husband.

(Ephesians 5:25-33 ESV)