Mathematical logic is a branch of mathematics that takes axiom systems and mathematical proofs as its objects of study. It provides guidelines for the development of information science and technology. This book, with 10 chapters, presents basic principles and formal calculus of mathematical logic systematically. The first five chapters cover the core contents of classical mathematical logic, including the syntax and models of first-order languages, formal inference systems, computability and representability, and Godel's theorems. The contents of the last five chapters are extensions and developments of classical mathematical logic. This part elaborates version sequences of formal theories and their limits, the system of revision calculus, proxchemes (formal descriptions of proof methods and strategies) and their properties, and the theory of inductive inference. It also describes the paradigm of environments of three kinds of languages and the basic principles of metalanguage environments and addresses the workflow of scientific research in the information era. The first five chapters of this book may be used as an undergraduate text in mathematical logic and the last five chapters may be taught to graduate students in relevant disciplines. The book may serve as a valuable reference for graduate and undergraduate students and researchers in mathematics, information science and technology, and other relevant areas of natural sciences.