The notion of the organism has a somewhat ambiguous status in Kant’s philosophy. On the one hand it belongs to natural science, on the other hand it is based on an analogy with the structure of reason. Biology therefore has a peculiar place among the sciences according to Kant: it is a natural science constituted by the use of a regulative maxim. The present study places Kant’s views on biological teleology in the larger context of transcendental idealism. It consists of five essays. The first one treats the notions of things in themselves and appearances, arguing for an interpretation in terms of two aspects or perspectives rather than two worlds. The importance of the discursivity of our cognitive capacity is stressed, as well as the need to separate Kant’s various reflective perspectives. In the second essay this interpretation is applied to the third section of the Groundwork, arguing that this text does not belong to theoretical metaphysics, but rather to the articulation of a specifically practical perspective. The third essay discusses similarities and differences between Kant’s a priori conditions for cognition and conceptions of innate ideas in the rationalist tradition. Kant’s comparison of the system of categories with the biological theory of epigenesis is considered in connection to eighteenth century theories of generation. The comparison is viewed as an analogy rather than as a naturalistic theory of the a priori. In the fourth essay Kant’s account of functional attribution in biology is explicated in the context of the present day debate of the issue. It is claimed that Kant’s neo-Aristotelian approach avoids some of the difficulties in the dominant naturalistic accounts of today. Kant’s view differs from the Aristotelian in that it involves a distinction of levels, making it possible to take functional attributions on the one hand as objective from the standpoint of biology but on the other hand as having a merely regulative status from a philosophical point of view. In the fifth essay an interpretation of the antinomy of teleological judgment in the Critique of Judgment is offered. The antinomy is taken to consist in the dialectical tendency to treat the regulative maxims of teleology and mechanism as constitutive principles. The difference between the discursivity of the human understanding and the idea of a non-discursive understanding, an important theme in Kant’s solution of the antinomy, puts the question of biological teleology in relation to central tenets of transcendental idealism.