First and foremost, a divorce actually “ends” or terminates a legal marriage whereas an annulment declares that the marriage never legally existed in the first place and that perhaps is the key to understanding the difference between the two.
Divorce relies on the fact that there is a legal marriage in place. And although it returns the parties to single status, it does not “undo” the marriage but rather stops it from continuing.
Annulment works just the opposite and relies on the idea that the marriage either shouldn’t or wouldn’t have taken place if all the facts had been on the table. This assumes that while a wedding may have occurred, there was never actually a legal marriage to terminate and thus all that is needed is to officially declare the union to be void or voidable.
A void marriage is one that was never legal to start with, such as in the case of a marriage of close relatives or parties who were underage. A voidable marriage is one that could be declared void because of specific facts but requires the parties to make a request to have it declared void. For example, if a man marries a woman who is infertile, many states allow him to ask for an annulment if the infertility was not revealed before the wedding. However, if the man finds out and continues to live with the woman as husband and wife, the “voidable” circumstance no longer exists and the marriage is considered to be valid.
Which brings us to the second major difference between divorce and annulment: the grounds (reasons). Like divorce, annulments have a specific set of grounds that the states will consider in an annulment hearing but where divorce grounds deal with situations, behaviors and circumstances that make the marriage no longer viable, grounds for annulment focus on reasons that prove the marriage never should have occurred in the first place.
In addition, while child custody, visitation and support are addressed in an annulment, alimony is typically not an option since the parties will have no financial obligation to each other once the marriage has been declared “null”. Some property division issues can also be addressed, specifically if the couple was married long enough to acquire some notable marital property. In general, however, the courts try as best they can to allow both parties to simply “leave with what they brought”.