This volume is an analytical exposition of the main ideas of Ingarden's epistemology, based generally on material previously unpublished or accessible exclusively in Polish. It is directed primarily to phenomenologists, but is also addressed to analytic philosophers interested in epistemology and in ontology of intentionality. Ingarden's epistemology, his theory of intentionality and the general aspects of his ontology are presented in relation to the Husserlian and Brentanian traditions and analyzd with the conceptual tools of contemporary analytical philosophy. Ingarden's epistemology is a discipline resulting from the fusion of Husserl's phenomenological method with the precise ontological framework developed by Ingarden. It contains two branches: the pure and the applied epistemology. The pure epistemology, being an absolute Cartesian discipline, formulates the definition of knowledge and rests on the peculiar self-referring state of mind called "die Intuition des Durchlebens". But the applied epistemology that investigates the concrete cases of (alleged) knowledge is an empirical, fallible and hypothetical science.