The idea of intentionality becomes fruitful for the first time when seen in connection with the methodological first principle of Husserl’s phenomenology, namely the phenomenological reduction. Husserl developed this principle in 1907 in the context of the epistemological problem of transcendence. In the following we shall examine what the idea of intentionality can accomplish with respect to the problem of transcendence. We want to limit ourselves, however, to a special problem sphere, namely, the constitution of material nature.