An Apostille is similar to notarization to certify a document, but intended for use in another country. Apostille is defined by a Hague convention between nations, and certifies that a notarized document in the originating member nation is true and suitable for use in another member nation. One might, for example, get Apostille certification of a marriage certificate to verify one's marriage elsewhere. The document, in English, would be trusted as authentic — though might additionally need a sworn translation into another language to be actually useful in that other nation.
The California Secretary of State is the certifying authority for the state. They run periodic pop-up locations in major cities for people to bring in their documents. In December of 2024 I tried to use one of these pop-ups in San Francisco, but the line was 3+ hours and I gave up before getting to the front.
One can instead mail documents to Sacramento, with a cover letter and return envelope. At the time of this writing the cost is $20 per document. I mailed in documents with a check on December 9th 2024, and received an Apostille dated December 21st. The documents arrived at our home on December 26th, slightly slowed by Christmas. So, expect roughly a two week turnaround.
