In this book, Paulo Guilherme Santos studies diagonalization in formal mathematics from logical aspects to everyday mathematics. He starts with a study of the diagonalization lemma and its relation to the strong diagonalization lemma. After that, Yablo's paradox is examined, and a self-referential interpretation is given. From that, a general structure of diagonalization with paradoxes is presented. Finally, the author studies a general theory of diagonalization with the help of examples from mathematics. Contents Diagonalization in Mathematics Diagonalization Lemma Fixed Point Theorems Paradoxes: Liar, Yablo's Paradox, Curry's Paradox Target Groups Researchers and students in the fields of mathematics and philosophy The Author Paulo Guilherme Santos is currently a PhD student at FCT, Universidade Nova de Lisboa, Portugal and at University of Tübingen, Germany. His field of work is logic, e.g. formal arithmetic, provability logic, provability predicates, and paradoxes.