The book discusses major topics in complex analysis with applications to number theory. This book is intended as a text for graduate students of mathematics, undergraduate students of engineering and researchers in fields of complex analysis and number theory. This theory is a prerequisite for the study of various areas of mathematics, including the theory of several finitely and infinitely complex variables, hyperbolic geometry, two- and three-manifolds, and number theory. In addition to solved examples and problems, the book covers most topics of current interest, such as Cauchy theorems, Picard's theorems, Riemann-Zeta function, Dirichlet theorem, Gamma function, and harmonic functions.