This subject has come up before and there seems to be a great deal of confusion about it. Since marriage licence bonds are something that many people will encounter as they search for pre-1837 marriage records, I thought this might be a good time for a more detailed explanation.
As Paul has explained, marriages were either by banns or by licence. The great majority of marriages were by banns. The couple's intention to marry was announced on three Sundays in their
parish church or churches---to allow anyone knowing of a "just impediment" to declare it.
Licences were issued by Church authorities and enabled people to marry immediately, without banns and in a church other than their parish church, if they so wished.
People chose to be married by licence for many reasons:
1) It was quicker, no time for the village to gossip, if there was something socially embarrassing about it. If they were in a hurry for any reason, the marriage could take place immediately, even in the religious seasons of prohibition (Lent, Advent,etc.)
2)the bridegroom might be likely to be suddenly called away ( a soldier or sailor)
3)the case a minor, requiring parental consent, (apparently they could marry by banns, but usually it was by licence).
4) either bride or bridegroom was only a temporary resident, living far from their home parish which would make it difficult to have banns read.
5) According to most authorities on the subject, the most common reason for marriage by licence(at least in the late 18th and 19th century was that it was the preferred way of the upper classes(more dignified and private). Because the upper- class did it, the aspiring lower middle-class did it too.
Before a marriage could be issued by Church authorities, it was necessary for the couple to make an allegation, a declaration on oath of their freedom to marry, i.e. they were of full age or if not had parental consent and were single or widowed. Two or more bondsmen were required to witness this allegation. Bondsmen would be required to pay a fine if any part of the allegation proved to be false. The bondsmen were often relatives or friends of the couple.
Sometimes the bridegroom's employer or another respected person such as a vicar or local businessman would act as bondsman.
As far as I know there was no fine imposed if the couple did not go through with the marriage. In fact is was not really all that rare for people to have second thoughts or give in to parents who did not approve. I know that it happened in my family---twice!
Marriage Licence Bonds give the names of the couple, age (sometimes), occupation, place of residence and place of birth. They do not include birth dates or any information about parents except in the case of minors. Bonds were kept by the archdeaconry or diocese and many have survived.
If church registers have not survived, bonds are sometimes the only record of a marriage. Not many licences have survived. After being
presented to the vicar who was to perform the marriage, they were discarded or taken home by the happy couple.
I hope this helps to clarify the issue to some extent and that I did not leave out something important in my haste.