The tax identification number (SteuerID) is a uniform identification number for tax purposes throughout Germany. The 11-digit number is unchangeable, unique and permanent.
You can apply for the tax ID directly at the Federal Central Tax Office. You may also have already received it in a letter. If you can no longer find it, you can simply look at the income tax certificate from your last job or the last tax assessment notice.
Basically, the notification letter of the tax ID looks something like this:
If you have any further questions on this topic, click Submit a Request.