From Leibniz, through Kant, Frege and the "Booleans" to Husserl, this book is offered as a contribution to the conceptual understanding of symbolic knowledge, the kind of knowledge obtained by means of symbols. Some traditional problems of logic, philosophy of formal sciences, epistemology, philosophy of language, metaphysics and philosophical methodology are also dealt with here; among them, problems concerning content and form, signs and representation, structural knowledge and isomorphism, language and calculus, and real and ideal elements. Despite its multiple authorship, the book has stylistic and thematic unity, and can be of interest to a potentially large philosophical audience. The authors teach in Brazilian and Argentinean universities, conducting their researches mainly in the philosophy of formal sciences.