This book is dedicated to the subject of the Gamma function and related topics. The Gamma Function is primarily intended for advanced undergraduates in science and mathematics. It is concise yet thorough and covers each of the most important aspects of the Gamma function. The Gamma function has important applications in probability theory, combinatorics and most, if not all, areas of physics. A large number of proofs and derivations of theorems and identities are covered in the book including: Analytic continuation of the factorials, properties via complex analysis, Holder's theorem, the Bohr-Mullerup theorem, the Beta function, Wallis's integrals, Wallis's product, product & reflection formulas, half-integer values, digamma and polygamma functions, series expansions, Euler-Mascheroni integrals, duplication & multiplication formulas, the Gamma and zeta function relationships, Hankel's contour integral representation, Stirling's formula, the Weierstrass factor theorem and the Mittag-Leffler theorem.