A credit freeze locks your credit file so no lender can pull it. No pull, no new account. That's the whole mechanism, and it's the single most effective thing a regular household can do against identity theft.
Federal law made freezes free at all three bureaus back in 2018. Free to place, free to lift, free to put back. If a site asks you for money to freeze your credit, you're on the wrong site.
You have to do it three separate times, once each at Equifax, Experian, and TransUnion, because they don't talk to each other. Each one takes a few minutes online and gives you a PIN or an account login you'll need later. Save those somewhere you'll actually find them in two years.
A freeze doesn't affect your existing accounts. Your cards keep working, your score keeps updating, and your mortgage servicer keeps reporting. It only blocks new credit applications.
A freeze is not the same as a fraud alert or credit monitoring. A fraud alert asks lenders to verify your identity and expires after a year unless you renew it. Monitoring services tell you after something has already happened. The freeze is the one that stops the account from being opened at all, and it's the only one of the three that's free and permanent.
When you do apply for something, you thaw the file. You can lift it for a set window, a few days or a week, or lift it at one specific bureau if the lender tells you which one they pull. Online thaws take effect in about an hour. Plan for that before you sit down at a car dealership, because doing it in the finance office with a salesperson watching is how people end up skipping it entirely.
Freeze your kids' files too. A child's Social Security number is attractive to a thief precisely because nobody checks it for eighteen years. The bureaus have a separate process for minors that takes documentation and a little more patience.