Reinhart Koselleck is among the most original German theorists of history and historiography. His international reputation is due in part to his contributions as theorist and editor of the remarkable lexicon Geschichtliche Grundbegriffe (GG). The GG is an exceptional reference work that goes far towards realizing Koselleck's program and distinctive version of Begriffsgeschichte (the history of concepts, conceptual history). What is presented here is a translation in full of Koselleck's own entry on Krise (crisis). Few articles in the GG demonstrate more successfully Koselleck's theoretical concerns, his method, and innovative use of sources.