I have been separated from my spouse for a few years and do not have any of her information such as her social security number. We are still legally married. What do I do

[brandanherman]

How do I file without her personal information? I do not have anyway of contacting her.

[Mike9241]

if you pay more than 1/2 the cost of keeping up a home for yourself and a child who lived with you for more than 6 months in 2021, you can file as head of household. your "spouse's" info is not needed. otherwise. the only options are a joint return or married filing separate (MFS). MFS will require you to mail in your return and attach a letter of explanation as to why your spouse's required info wasn't furnished.

[SweetieJean]

How have you filed in recent years since the separation?  Do you have any old tax returns or other documents with her SSN?  We cannot give legal advice here, so I suggest you see a lawyer since still being legally married affects lots of things besides taxes.