A prenuptial agreement is a contract signed before marriage that sets out how property, debt, and financial matters will be handled — both during the marriage and if it ends. The stigma around them has outlasted their actual usefulness.
What a prenup actually controls
A prenup can define what counts as separate versus marital property, protect a business or inheritance you're bringing into the marriage, set expectations around debt each person brought in, and establish (within legal limits) spousal support terms if the marriage ends.
What a prenup can't do
Prenups generally can't decide child custody or child support in advance — courts decide those based on the child's best interests at the time, not on an agreement signed years earlier. Terms that are clearly one-sided or signed under pressure are also the most common reasons a court throws one out.
Full financial disclosure is what makes it enforceable
The single biggest reason prenups get successfully challenged is incomplete financial disclosure — one party hiding assets or debts before signing. Both sides listing everything honestly, in writing, is what gives the agreement its strength later.
Timing matters more than people expect
Signing a prenup days before the wedding, under obvious time pressure, is a common ground for later challenges. Courts look more favorably on agreements signed with enough time for both parties to actually review and negotiate the terms.