Hi,
We got married in 2010 and my wife resigned and moved from IL to CA in Sept 2010. She changed her last name with SSN office in Nov 2010, but she forgot to tell her ex-employer. They issued the W2 with her old last name. So what name do we use for filing - her old last name or new last name. As of Nov 2010, the SSN office has her new last name.

Thanks,
Sivaram

She files taxes in her legal name. She includes W2's in her previous name. The SS number is the same.

I work under my previous name. My married name is my legal name. I file taxes under my legal name (using the old name on W-2's and 1099's).

One thing to add - she should tell the payroll department to update her name in their records so it agress with her SS card (and other legal docs like her passport and driver's license). If professionally she still wants to use her old name on business cards and the like she can certainly continue to do that, but if she travels for work be aware that the TSA is pretty sticky these days about names matching between tickets and ID.