The concept of nonpropositionality covers the vast field of those aspects of knowledge and experience that cannot be captured by a truth-functional approach or escape conceptual analysis. The book is confined to questions of theoretical philosophy. Its first part provides an orientation within the nonpropositional jungle by critically following a historically beaten track: the philosophy of Gottlob Frege. It not only explains the propositional focus of Frege's epistemology, logic and philosophy of language against the historical background of psychologism but focuses on the limits of this propositional approach. The critical analysis of Frege's logicist project centres on its foundational basis: definitions, logically primitive terms, elucidations of these terms as well as aspects of what Frege calls ,colouring'. The second part of the book echoes many of the central elements which mark the limits of Frege's propositional conception by dealing with the systematically pivotal role that the concept of nonpropositionality plays in contemporary analytical philosophy, especially within epistemology and philosophy of mind. Two main areas stand out: theories of perception and the discussion of inner experience. The focus here is on non-epistemic conceptions of seeing, the non-conceptual content of experience as well as on phenomenal consciousness and self-consciousness. The pivotal claim is that the nonpropositional constitutes the basis of and a necessary condition for the propositional. Any attempt to embark on an analysis of the propositional and of propositional knowledge will float in the air unless the nonpropositional grounds are systematically secured. The book aims to close this gap.