This accessible and wide-ranging introduction to critical theory provides a comprehensive overview of the practice, role, and importance of theory across the humanities and social sciences. It not only maps a notoriously complex area, but it also enables the reader to take the arguments and apply them in practice. Starting with an explanation of how theory relies on implicit assumptions that inform interpretations, the book moves on to depict the long-term philosophical problems that have fed into much 20th century thinking and also more recent debates. The philosophical grounds of contemporary thought are traced from Plato through Descartes to the work of Heidegger and Freud and on to recent developments in structuralism and deconstruction that critically revise many of the previous terms of debate.