I've been searching the forum and the Google Oracle for the past 2 hours and still can't quite find the answer I need, so I'll post my question here in hopes of getting some clarification.
I moved to Germany in 2008 as a student and was issued an 11-digit "Persoenliche Identifikationsnummer" from the Bundeszentralamt for Steuern in February 2009 while living in Frankfurt. I didn't earn income until Summer 2009, when I was a freiemitarbeiter (freelancer-like arrangement in which my employer made some contributions to Versicherungen) in Bonn. After being told that the Letter with the Personliche Identifikationsnummer was not what I needed, and that I needed a Lohnsteuerkarte, I applied for one in Bonn. This Lohnsteuerkarte has nothing on it that is labeled "Steuernummer," but it does include the same 11-digit number that was listed as my Persoenliche Identifikationsnummer - on this form it's called simply "Identifikationsnummer."
Fast forward to now, where I am living in Bonn and recently did some Nebenjob-type work (transcribing an interview for someone) for which I need to send an invoice with my Steuernummer.
So, in my case, is my Steuernummer the same as the "Persoenliche Identifikationsnummer"/"Identifikationsnummer"? Or is it a different thing entirely? Where would I find it on a Lohnsteuerkarte?
The Identifikationsnummer is useless and superfluous on an invoice. You must use either your Steuernummer, or your Ust-ID-Nummer (if you have one), or if you feel like it, then both (UstG §14, Abs 4, Nr 2)
The Identifikationsnummer is unique to an individual and does not apply to companies or other legal trading entities. It is therefore possible for a person with one Identifikationsnummer to have or share multiple Steuernummern, hence they are unique to the trading entity and should be used on any invoice related to that entity.
And what is the Ust-ID-Nummer mentioned above? Is this also something that would show up on a Lohnsteuerkarte?