The original essays in this volume present cutting-edge research on unstructured theories of propositional content. Unstructured theories have traditionally played a central role in linguistics, especially formal semantics, and both the philosophy of language and philosophy of mind. The volume explores a wide range of themes related to unstructured content such as the continued controversy over whether unstructured theories individuate contents too coarsely compared to other theories of propositional content, and applications of unstructured theories to various topics. Topics to which unstructured theories are applied include rationality, epistemic commitment, semantic expressivism, relevance, and attitude ascriptions. Theories of unstructured content discussed include traditional theories according to which propositions are sets of worlds, as well as contemporary theories such as truthmaker semantics. The volume contains contributions from different theoretical perspectives, including perspectives sympathetic to unstructured theories of content and perspectives that are skeptical, as well as perspectives from different methodological backgrounds, with philosophy, logic, and linguistics all represented. With contributions from leading scholars in philosophy and linguistics, this volume will be required reading for anyone working on the nature of propositional content. It will also be of interest to those working on related issues in logic, metaphysics, and the philosophy of mind.