This book is a compilation of the authors most important papers about the contributions of Bertrand Russell, Kurt Gödel, and Alfred Tarski to the philosophy of logic and mathematics. It also includes a personal reflection of the authors approach to his field of research. The papers in this book have been assembled to convey key elements of the authors research on the published and unpublished materials of the three greatest logicians of the twentieth century. Francisco Rodríguez-Consuegra is well known in the field of the History and Philosophy of Logic and Mathematics, mostly due to his former books: The Mathematical Philosophy of Bertrand Russell (Birkhäuser, 1991) and Kurt Gödel, Unpublished Philosophical Essays (Birkhäuser, 1995). Throughout his career, the author visited and worked in depth in the Russell Archives (Hamilton, Canada), the Gödel Nachlass (Princeton, USA), and the Tarski Papers (Berkeley, USA). This book is of interest to students, professors, and researchers in the history of logic and mathematics, philosophy of logic and mathematics, and general history and philosophy of science.