'Is reason then alone baptized, are the passions pagans?' By placing Edward Young's question on the frontispiece of Either/Or, Søren Kierkegaard announces a problem that runs throughout his authorship: what role do the affects play in human existence? His answer helps explain his enduring importance for modern philosophy. Across works such as Either/Or, The Concept of Anxiety, and The Sickness unto Death, Kierkegaard develops powerful accounts of affects such as irony, melancholy, anxiety, and despair, while also exploring the affective dimensions of philosophical writing itself. This Element examines Kierkegaard's treatment of affectivity across his writings and across individual affects. It argues that his account is organised around a tension between two forms of affective life: baptisable affects that can be transformed and integrated into the project of becoming a self, and non-baptisable affects that resist such transformation and threaten to derail it.