IPA is phenomenological in that it wishes to explore an individual’s personal perception or account of an event or state as opposed to attempting to produce an objective record of the event or state itself. Thus, one important theoretical touchstone for IPA is phenomenology, which originated with Husserl's attempts to construct a philosophical science of consciousness.
At the same time, while trying to get close to the participant's personal world, IPA considers that one cannot do this directly or completely. Access is dependent on the researcher’s own conceptions which are required to make sense of that other personal world through a process of interpretative activity. A second important theoretical current for IPA is, therefore, hermeneutics- the theory of interpretation.
IPA is also a strongly idiographic approach concerned with detailed analysis of the case either as and end in itself or before moving to similarly detailed analyses of other cases.
Link to the IPA@BBK webpage to see its activities
Link to Jonathan A Smith's webpage at Birkbeck