The present study seeks to accomplish three goals: to shed light on the problem of reason in Husserl’s co-inherited philosophical project , to elucidate his transcendental critique of reason, and to present Husserl's idea of reason in its distinctive features. A historical excursus first provides a frame to understand the necessity of a critique of reason, its proper subject-matter, and its function for the project of genuine philosophy. In particular, this historical reflection identifies the form that a critique must assume in order to fulfil its philosophical-scientific task. The focus is then directed at Husserl's methodological recalibration of the problem of reason. Husserl's ‘ prinzipielle Kritik ’ is elucidated in his transcendental reassessment of the headings ‘reason’ and ‘unreason,’ and is thought in connection to the concept of Selbstbesinnung . Lastly, Husserl’s idea of reason is reconstructed in relation to, and in disambiguation from, the concepts of self-evidence, logos, synthesis, fulfilment, positing, etc. Reason, as teleological rule and structural form of transcendental subjectivity, is clarified in its dependence on, and irreducibility to, the problems of constitution and in light of the question of its objective/subjective character.