The abbreviation K. u. K. (or K. und K., K. & K.) stands for kaiserlich und königlich -- German for Imperial and Royal.

The phrase refers to the so-called "Dual Monarchy" of Austria-Hungary from 1867 to 1918: The Emperor of Austria also reigned, in personal union, as the King of Hungary. All government acts took place in the name of "His Imperial and Royal Majesty": most of the time abbreviated to "k. u. k.". Also, all governmental institutions and offices had a name prefixed with "k. u. k.". Austria-Hungary, also known as the Dual monarchy (or: the k. ... 1867 was a common year starting on Tuesday (see link for calendar). ... 1918 (MCMXVIII) was a common year starting on Tuesday of the Gregorian calendar (see link for calendar) or a common year starting on Wednesday of the Julian calendar. ... The title of Emperor of Austria was proclaimed in 1804 by the Habsburg Holy Roman Emperor, Francis II, who feared for the future of the old Reich in the face of Napoleons aggressions, and wished to maintain his imperial title in the event that the Holy Roman Empire should... A personal union is a political union of two or more entities that, internationally, are considered separate states, but through established law, share the same head of state —hence also whatever political actions are vested in the head of state, but no (or very few) others. ... This is a list of all rulers of Hungary since Árpád. ...

The ubiquity of this phrase in all administrative matters made it a synonym for the Dual Monarchy, often referred to even today as "the k. u. k. monarchy".

In Czech the equivalent abbreviation appears as "c. a k.", in Polish – as "C. i K." or "CK".

Arising from the term "k.u.k." we find the name "Kakania", sometimes used to describe the Empire as a state of mind, bureaucratic and with a very stratified formal society (e.g. in work of Robert Musil). The name "Kakania", by means of a childish Czech-language pun, also expresses the idea of "shittiness". Robert Musil (Klagenfurt, Austria, November 6, 1880 – April 15, 1942 in Geneva, Switzerland) was an Austrian writer, author of the unfinished long novel The Man Without Qualities (in German, Der Mann ohne Eigenschaften), one of the most important modernist novels. ...

Political importance of the "U"

Prior to 1867, the collection of territories under the control of the Habsburg monarch in Vienna used the style of the kaiserlich-königlich (Imperial-Royal) realm, (abbreviated k.k. or k-k) with the hyphen connecting the terms and implying an indifferent or even interchangeable distinction between the various lands. The Habsburg monarch ruled Austria as Emperor, and the kingdoms of Bohemia and Hungary as King. Flag of the Habsburg Monarchy; also used as the flag of the Austrian Empire until the Ausgleich of 1867. ... Vienna (German: Wien [viːn]; Slovenian: Dunaj, Hungarian: Bécs, Czech: Vídeň, Slovak: Viedeň, Romany Vidnya; Croatian and Serbian: Beč) is the capital of Austria, and also one of the nine States of Austria. ... An emperor is a (male) monarch, usually the sovereign ruler of an empire or another type of imperial realm. ... Bohemia This article is about the historical region in central Europe; for other uses, see Bohemia (disambiguation). ...

After the crisis and compromise in Hungary resulting in the Ausgleich of 1867, the nationalist Hungarians rigidly insisted upon the und ("and") replacing the hyphen in all usage, in order to indicate the independent nature of their relationship to the other (Austrian) lands. The German term Ausgleich (Hungarian kiegyezés) refers to the compromise or composition of February 1867 that established the Dual Monarchy of Austria-Hungary, which was signed by Franz Joseph of Austria and a Hungarian delegation led by Ferenc Deák. ... 1867 was a common year starting on Tuesday (see link for calendar). ...