Both.

These are two different titles; therefore you have to translate both as "professor doctor NN".

I agree with your gut, JeffreyJohn. Although Werner and Ralf-NZ are technically correct, this type of German combination title seems weird to many English-speaking ears.

My rule of thumb is that "Professor" is used primarily when discussing teaching responsibilities and "Doctor" is used for almost everything else.

You have to balance the need to be totally faithful to the German against the need to give the reader something they can understand. I'd probably go with "Dr." in this case. If need be, I suppose you could put "Professor of such-and-such" after his name.

I'd be interested in hearing what other English speakers have to say.

I agree with GeorgeA. Double titles of this type do not sound right in English. In a North American context, anyway, you can be called "Professor" without holding a doctorate. Go with "Dr.", adding "Professor of..." after the name if you deem it necessary.

See also: related discussion: prof. dr.

(and links given within) . . .

Some of my mentors are Professor Dr. and we call them Prof but they always name their full title as well. So I figure it must mean something to them :D
There's no harm in that and at least in Texas this combination is wellknown.

@Spectra: I can imagine the following introduction:

Student: Mr. Smith, I'd like to introduce you to my professor, Dr. Jones.
Mr. Smith: Pleased to meet you, Dr. Jones.

Yes, "professor" and "Doctor" appear together in this dialog. And yes, Dr. Jones is probably pleased to hear both his role as "professor" and his degree mentioned.

But in this case "professor" refers to Dr. B's duties, not his title. I think it is unliekly that you'll ever hear a native speaker introduce someone as "Professor Dr."--even in Texas.

I agree with you. But.
In a clinic a professor is a doctor. Would take too long to name all titles during treatments. When it comes to universities it is a Professor Doctor xxx. Especially when we talk about a diploma, I'd translate all titles. But I also don't believe that he would feel humiliated just by calling him "only" Doctor.

I agree that Prof. Dr. would sound odd to Americans, but here in Germany, professors earn this degree in a similar manner as they did their doctorate. Odd, or not, when I sent a letter from "my" Prof. Dr. to someone in the US, it was signed "Prof. Dr. X." (this was in the pre-Internet era, where I'd prepare business letters for him to sign). He would have been rather upset, had his hard-earned "Prof." been omitted.

There are many, many old discussions on this in the archive (Suche in allen Foren).

It not only sounds weird, it's a mistake to write these two forms of address together in English. It's just not done. In German you can also write 'Herr Dr.' or 'Frau Dr.,' but no one would ever write *'Dr. Mr.' or *'Dr. Ms.' in English. (One of the few traditional exceptions is 'Rev. Dr.,' but even that is now usually replaced by 'Dr.' alone, at least in AE.) That's just not how English names work. It does not mean that professors addressed in German have earned any extra title that their English colleagues lack, or that professors addressed in English are being deprived of any recognition due them, it's just a different convention.

Professor is the higher title, so in formal English, 'Prof. X' takes precedence. Contrary to some misleading comments above, it is assumed that virtually everyone who holds a professorship also has a doctorate, so it's not necessary to add the lower title of 'Dr.'

Yes, it's also fine to address a professor as 'Dr. X,' especially in conversation (partly just because it's shorter). And yes, in a business letter there's usually an extra line under the signature giving the professor's full title, so it's not essential to use 'Prof.' in front of the name:

Dr. John Doe
Professor of Applied Mathematics

That's probably the easiest way to solve this particular issue in practice.

Surely I need not point out that all of this is as true in Texas as anywhere else.

It is by no means true that those styled "Professor" are assumed to have a doctorate. Indeed, in my personal experience, "Professor" is used in some North American academic institutions as a lesser title only for those who do not hold a doctorate. Clearly, the practice varies from place to place.

Ich habe den Eindruck, dass hier zwei unterschiedliche Diskussionen gefuehrt werden, wobei die Anfrage noch ein drittes Thema aufweist.
Die erste handelt von der Uebertragung dieser Titelkombination in verbaler Kommunikation.
Die zweite beschaeftigt sich mit dem Thema, wie man diese Titelkombination auf Briefen uebersetzt/uebertraegt.
Die urspruenglicher Anfrage jedoch besteht darin, wie man dies von einer Urkunde her uebersetzt.
Vielleicht koennten einige, die bisher kommentiert haben, doch auch noch einen Beitrag liefern, der staerker die urspruengliche Fragestellung beruecksichtigt.

>> in my personal experience, "Professor" is used in some North American academic institutions as a lesser title only for those who do not hold a doctorate

Sorry, but I just find that very hard to believe. It really would surprise me, at any reputable college or university. It seems at least possible that you misunderstood the title and drew the wrong conclusion, or that the people at the academic institution in question were just mistaken in their usage, especially if it was a small college or a community college.

It's also possible that a private high school, as opposed to a college or university, might call ordinary teachers professors, just out of custom, but that's a completely different context.

In any case, as Ralf points out, none of that is relevant to JeffreyJohn's example, where the person is clearly a professor with a doctorate, so 'Prof. X.' is clearly correct.

However, it's also true that in English-speaking universities, being a university dean or president is normally a full-time job, so although it's often held by someone who has previously been a professor, they might not retain that title on taking the higher administrative office, unless they continued teaching students and doing research as well. So perhaps I should have added that administrators are often just addressed as 'Dr.':

Dr. Fred Smith
President, University of X

Dr. Maria Jones
Dean of Graduate Studies

That's actually what I would expect to see under a signature on a diploma, so in that sense, I agree with JeffreyJohn's gut feeling.

So the short answer: In English, either 'Prof. X' or 'Dr. X,' depending on context, but never *'Prof. Dr. X.'

W"are es m"oglich zu schreiben, z.B. in der Zeile unter der Unterschrift:

Prof. Fred Smith, Dr.

oder, wenn das genaue Doktorat bekannt ist

Prof. Fred Smith, Dr. rer. pol.

analog zu

Prof. M. W. Travers, D.Sc., F.R.S.
Sir Robert Robertson, K.B.E., DSc., F. K.S.
Prof. F. G. Donnan , C.B.E., Ph.D., F.R.S.
Prof. C. H. Desch, D.Sc., F.R.S.

http://www.rsc.org/delivery/_ArticleLinking/D...

Allerdings fehlen dann in der oben vorgeschlagenen Aufz"ahlung die weiteren Abschl"usse und Titel.