If you are a U.S. citizen working in Berlin and paying German income tax, you will not be double-taxed on the income. The USA will give you credit for the tax paid in Germany. See Form 1116. Others have mentioned the Foreign Earned Income Exclusion. See Form 2555.

You will, however, pay two metric shit-tonnes in professional fees getting your U.S. tax returns prepared because the international tax rules are so ridiculous. The operating principle in U.S. tax law is "If you are doing something abroad, you must be Mafia ^H^H^H^H^H a drug lord ^H^H^H^H^H a thieving bastard tax cheat ^H^H^H^H^H^H terrorist." (The Poster Child of Evil has changed over the years, but the pig-headedness has remained constant).

Disclaimer: I am an international tax lawyer.