Hi,
I have landed in the US on march 2013. I want to apply tax id for my wife & child. Could you please send me a mail with the details w
1)What are all the documents I should send.
2)What are the forms I should fill
3) Which address I should sent the documents for processing?
4) Is that fine to send the documents via postal to the IRS office or it is good to go to IRS office and apply for tax id?

As my dependents did not have the tax id till now, am I eligible to mention my dependent details while filing the tax for this year?

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It is probably most advantageous for you to file jointly with your wife, filing Form 1040 with Form 1116 to claim the Foreign Tax Credit.  Form 1116 is required because you must claim ALL world-wide income earned in 2012, and the Form 1116 allows you to claim a credit for the income taxes paid to your home country. Note that you must WAIT until 2014 before you can file this joint return.

You will need to apply for an Individual Tax Identification Number (ITIN) for your wife by submitting Form W-7, and that process has undergone some radical procedural changes this past year.  Instead of the simple notarization process, the IRS now requires that your home country certify the photocopy of your passport as a true copy.  This is due to rampant fraud in the ITIN submission process.  The notaries simply cannot tell the difference between a fake passport and the genuine passport.

FIRST ALTERNATIVE: This certification can be done by the Indian (I assume you are from India) embassy in Washington, D.C. or at one of the consulates in San Francisco, Chicago, Houston or New York.  Assuming you do NOT want to drive there, you need to call the nearest consulate and arrange to have this process done via the mail.  Since you must wait until June to file, you have time to get this done (the process, done via mail, can take up to three months to complete). My clients to date have had the best results by mail with the San Francisco consulate, getting the certified passport photocopies in less than 3 weeks.

SECOND ALTERNATIVE: The IRS recently announced the opening of Tax Assistance Centers through which you may be able to have the passport verified as genuine, then submit the tax return and Form W-7 IN PERSON to be forwarded to the ITIN Processing Center in Austin, Texas for processing , without having to get the photocopies certified by your home country consulate.

You go to the TAC with your wife and child, their passports, the SIGNED Forms W-7, and the completed and SIGNED tax return.

The IRS official verifies the passport, asks a few questions, completes the certification paperwork, checks the Form W-7 and tax return, then returns the passport with a receipt for the tax return and W-7, which is sent to Austin, Texas for processing.

You leave the TAC with your wife and child, the passports and a receipt for the Forms W-7 and the tax return.

You would get the ITIN about six weeks after you left the TAC.

The list of the TACs are at the link below:
Taxpayer Assistance Center Locations Where In-Person Document Verification is Provided

The FINAL alternative is to mail in the actual passports themselves, something most of my clients are reluctant to do.