In short
Every other form in a bankruptcy case shows only the last four digits of a Social Security number. Form 121 is the one place the full number goes.
The court keeps it out of the public record. The full number is available to creditors, the U.S. Trustee or Bankruptcy Administrator, and the trustee assigned to the case, and to nobody else.
Who files it
Every individual debtor, in Chapter 7 and Chapter 13. In a joint case, one form covers both spouses.
What it asks
Part 1: Tell the Court About Yourself and Your Spouse if Your Spouse Is Filing With You
Full names, matching the petition.
Part 2: Tell the Court About All of Your Social Security or Federal Individual Taxpayer Identification Numbers
Every Social Security number or ITIN you have used, or a statement that you have none.
Part 3: Sign Below
A signature under penalty of perjury.
When it’s filed
With the petition, under Bankruptcy Rule 1007(f). It’s submitted separately from the public filing, and each court has its own procedure for that.
Related forms
The official form
Official Form 121 is one page long and is used in Chapter 7 and Chapter 13 cases. This guide describes the 12/15 revision, the date printed beside the form’s title. The federal courts publish the form and replace it when it changes, so their page always has the current one.
BK Prepare’s questionnaire builds the list of forms for a case from your answers, and includes this one when it applies.