If you’re getting married anywhere in the United States, the first step is to get your marriage license. The rules for doing so vary from state to state, with different minimum age, cost, number of witnesses, and blood test requirements. California, however, is the only* state that offers both a regular public marriage license and a confidential marriage license.

[*One other state, Michigan, has something called “secret marriages,” but unlike confidential licenses, secret marriages require a judge in a closed court to seal the court file, and the clerk has no record at all of the marriage.]

A confidential marriage license is legally binding, just like a public license, but it’s not part of the public record. Section 501 of California’s Family Code allows for the county clerk to issue a confidential license, and Section 511 states that these licenses are not open to public inspection, except by a court order. Public marriage licenses, on the contrary, allow anyone, for any reason, to look at the personal information that appears on the licenses at the County Clerk’s office. This information—the couple’s full names, dates and places of birth, parents’ full names, and any previous marriages—is private for confidential licenses.

But why does California alone offer this option? The origin of the confidential marriage license goes back to 1878, when it was meant for unmarried cohabitating couples in the state. Some of these couples lived in rural, remote areas that were inconveniently far from a church or court, but most simply “lived in sin” and/or gave birth to children out of wedlock. Shacking up was majorly frowned upon, so couples could maintain the appearance of respectability within their communities by keeping the details of their nuptials confidential. Confidential marriages were also a boon to the California legal system because inheritance and property rights were more clear-cut when the majority of people cohabitating and raising children were married.

Until the 1970s, confidential marriage was still an option, but it wasn’t widely taken advantage of as social mores shifted and it became less scandalous for unmarried couples to live together. In 1972, California state legislators changed the law so that laypeople, not just pastors, could perform confidential marriages, allowing couples to marry quickly (without getting their blood tested and waiting for the results) and privately. By the early 1980s, almost 1 in 3 marriages in California was a confidential one. Polygamists, minors, and people falsely claiming Social Security benefits took advantage of the confidential option, though, and the state legislature came close to doing away with it in 1984—it stayed alive by one vote. In 2012, approximately one fifth of all California marriage licenses issued were confidential.

To apply for a confidential marriage license today, a couple must swear that they live together, but it’s a technicality since the couple doesn't have to provide any proof and there is no required minimum length of time for cohabitation. In Los Angeles county, confidential marriage licenses are actually a little cheaper than a public license, but couples opting for the confidential route have to pay $14 to order a certified copy of their license and certificate, so the cost evens out. And since it’s private, no witnesses are needed to be present at the ceremony to sign the license. It’s not exactly clear why other states’ legislatures never added the option for a confidential marriage license after California instituted it, perhaps due to lack of demand. For now, if you want to get a confidential marriage license, you’ll have to do so in California.