The Kingdom of Ends (German: Reich der Zwecke) is a part of the categorical imperative theory of Immanuel Kant.
It is regularly discussed in relation to Kant's moral theory and its application to ethics and philosophy in general.
A Kingdom of Ends is composed entirely of rational beings, whom Kant defines as those capable of moral deliberation (though his definition expands in other areas) who must choose to act by laws that imply an absolute necessity.
These common laws, established by the categorical imperative, are the gauge used to evaluate the worthiness of an individual's actions.
When the kingdom's individuals live together by the categorical imperative—particularly Kant's second formulation of it—each one will treat all others as being ends in themselves, instead of mere means to achieving one's own pursuits.