The chapter will present the theoretical underpinnings of the genetic -phenomenological approach in existential psychotherapy . It starts with an introduction to the difference between the static and the genetic methods developed by Edmund Husserl. Secondly, the three main theoretical constructs underlying the genetic-phenomenological analysis are presented: inner time-consciousness theory , the experiential self and the theory of passive geneses . The goal of the chapter is to establish a basis on which to explain how both phenomenological methods can be applied to therapy and to make explicit the psychological phenomenological concepts that sustain the theory of this model of existential psychotherapy .