The book provides a comprehensive presentation of function theory, starting with the theory of Riemann surfaces, including uniformization theory, as well as a detailed discussion of the theory of compact Riemann surfaces, the Riemann-Roch theorem, Abel's theorem, and the Jacobian inverse theorem. This serves as motivation for a brief introduction to the function theory of several variables, followed by the development of the theory of Abelian functions up to the theta theorem. Subsequently, and motivated by this, an introduction to the theory of higher modular functions is provided.