Tax Identification Number
The tax identification number (IdNr.) is an 11-digit, non-“talking” number. It therefore contains no information about the taxpayer or the competent tax office.
With the introduction of the IdNr, the taxation procedure should be simplified and bureaucracy reduced. It facilitates communication in the taxation procedure, because it allows a clear assignment of tax returns, notifications and any correspondence. The IdNr therefore remains valid for a lifetime and does not change when moving or marrying.
(Quelle: www.bundesfinanzministerium.de)