“Unknowns” and “Black Swans” have become familiar terms in the public administration literature but tend to be used in different and often conflicting ways. This article provides a typology of the two terms, develops a framework for thinking about how their elements relate, and distinguishes four varieties of the Black Swan. Using the Challenger Space Shuttle disaster, 9/11, the recent international withdrawal from Afghanistan, and the trade boycott associated with the Danish cartoon controversy as examples, we examine how these four varieties may arise in public sector organizations. We offer recommendations on how such organizations might reduce psychological and organizational barriers to uncovering unknowns before they can go on to become Black Swans.