Jacobi’s influence on the founder of so-called existentialism, Søren Kierkegaard, has rarely been examined. This chapter explores Kierkegaard’s critical and somewhat polemical discussion of Jacobi’s notion of the “leap” in Concluding Unscientific Postscript, which not only shows that Kierkegaard was acquainted with Jacobi’s major work, Concerning the Doctrine of Spinoza but how it shaped Kierkegaard’s own particular development of the salto mortale.