The adjective kaiserlich-königlich (usually abbreviated to k. k. or k.k.) is German for Imperial-Royal and was applied to the authorities and state institutions of the Austrian Empire until the Austro-Hungarian Compromise of 1867, which established the Austro-Hungarian Empire. Thereafter, in what was now the Austro-Hungarian monarchy, the abbreviation k. k. only applied to the western half of the empire (Cisleithania or Old Austria) which became a real union and double monarchy. Common institutions of both halves of the empire were described from 1867 to 1918 as k. u. k. or "Imperial and Royal". Contrary to the regulations, the Common Army continued to use the abbreviation k. k. to describe itself until 1889.
The first k. (kaiserlich = "Imperial") referred to the title Emperor of Austria, the second k. (königlich) referred, from 1867, to the title King of Bohemia, which the emperor held in personal union.
Today, the abbreviation k. k. is often replaced by the easier to pronounce k. u. k. ("k and k"), but should however be clearly distinguished, historically and legally from it. The prefix k. u. k. (kaiserlich und königlich) only referred to the authorities and institutions of both halves of the empire. In terms and names preceded by k. u. k., the second k. (königlich) referred to the title King of Hungary which was borne by the Habsburg monarchs.
The abbreviation h. k. k., which was frequently used in connexion with the central ministeries, meant "high" imperial-royal (hohes kaiserlich-königliches), e. g. in h. k. k. Ministerium für Kultus und Unterricht, h. k. k. Statthalterei für Tirol und Vorarlberg, h. k. k. Ministerium für Handel und Volkswirthschaft, etc.