This book presents, in a systematic and almost self-contained way, the analogy between the Nevanlinna theory and Diophantine approximation. Although the emphasis is on Nevanlinna theory, both theories are presented in this book, including some results of recent research. We divide each chapter into Part A and Part B. Part A deals with Nevanlinna theory and Part В covers Diophantine approximation. At the end of each chapter, a table is provided to indicate the correspondence of the theorems.