||Metaphysical indeterminacy (MI) is indeterminacy that originates in the world, not in how the world is represented in thought or language. The way this general gloss gets specified depends on whether we identify the world with the totality of things, or the totality of states of affairs. If the world is the totality of things, MI will arises if some object is indeterminate. Object indeterminacy has been associated with indeterminacy in matters of identity, distinctness, composition, constitution, location, or existence. The very possibility of object indeterminacy is a highly controversial topic. If the world is the totality of states of affairs, metaphysical indeterminacy will arise if some state of affairs indeterminately obtains. Metaphysical indeterminacy of this variety has been ascribed to a number of domains, such as quantum mechanics, the future, morality, chances, causation, and lawhood. Throughout the 20th century, the very notion of MI used to be widely regarded as incoherent, if not unintelligible. Such worries have been mostly set aside by the bevy of theories of MI developed in the 21st century. Among the questions that remain open are the following: How is MI best characterized? What is the logic (or the logics) for reasoning about indeterminate subject matters? Is MI an actual, or merely possible phenomenon?