The longest officially used German word was:

Rindfleischetikettierungsüberwachungsaufgabenübertragungsgesetz

(63 letters)

Translation:

“Beef labeling monitoring delegation law”

This was the name of a law in the German state of Mecklenburg-Vorpommern. It referred to the delegation of tasks related to monitoring beef labeling, especially relevant during the BSE (mad cow disease) crisis. The law was abolished in 2013.

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But German allows theoretically endless compound words. A classic (but not officially used) example is:

Donaudampfschifffahrtselektrizitätenhauptbetriebswerkbauunterbeamtengesellschaft

(80 letters)

Translation:

“Association of subordinate officials of the main building for electrical services of the Danube steamship company”

This is a joke word created to illustrate how German compounds work. It’s not used in real life, but it’s popular in linguistic discussions and trivia.