This book introduces value distribution theory starting with a survey of two Nevanlinna-type main theorems and defect relations for meromorphic mappings from parabolic manifolds into projective spaces. Then the unicity theory of meromorphic functions or mappings is discussed systematically and the discussion also covers value distribution theory of algebroid functions of several variables and its applications in unicity theory. Audience: Graduate students and researchers involved in the fields of analysis, complex function theory of one or several variables, value distribution theory and analysis on complex manifolds.