The traditional type of marriage was called confarreatio. This was a marriage limited to Romans whose parents were also married with confarreatio. The wedding was an elaborate ceremony with the Flamen Dialis and Pontifex Maximus presiding, as well as ten witnesses. The woman passed directly from the ownership of her father to that of her new husband.
Divorce for confarreatio marriages, diffarreatio, was a difficult process and therefore rare.
Not much is known about how diffarreatio was carried out except that there was a special type of sacrifice that caused the dissolution of the relationship between the man and woman. She would then pass back into the ownership of her father
The most common type of marriage was coemptio. It represented a 'wife purchase', as the groom paid nummus usus, a penny, and received the bride in exchange.
While this purchase was not a real sale, it symbolized the traditional bride purchases of earlier societies. Only five witnesses were required and the wedding ceremony was much less formal than confarreatio, but the bride still passed to her husband's ownership.
A type of marriage that was obsolete by the end of the Republic was the Usus. This was a practical marriage that did not require an actual wedding ceremony. It was a transfer to the ownership of the woman to her new husband after they had been co-habiting. The only requirement for an usus marriage was that the man and woman live together for one full year. The woman would then pass into her husband's ownership.
If within that year the woman was away for three consecutive nights, she could not pass into the ownership of her husband by Usus.
There were also marital unions that did not require the women to pass into her husband's ownership.
In a free marriage, the wife would retain her independence. If the father was dead, and had so stipulated in his will, she would be suae iuris, responsible for herself. She, under suae iuris, could then manage her own property and even initiate a divorce.
Concubinatus was another alternative to marriage.
A concubine, or paelex, was a woman who had regular 'activities' with a married man. Often the man and his concubine would live together, but without the emotional bonding that characterized Usus marriages.
Children of this type of union were illegitimate, indicating that the relationship itself was not legitimate. If the couple did have an emotional involvment and there were no legal disqualifications to marriage, the relationship could become a matrimonium.
Concubinatus was an acceptable alternative unless her father gave the woman as a concubine because he could not afford a dowry for her (an embarrassment). While not an actual marriage, contubernium was a marital-like union often practiced by slaves. Again the underlying belief was cohabitation. This situation was not a permanent one, but existed only until both partners gained their freedom.