Pappus’s Theorem is simple yet very important and useful theorem contributed to Pappus of Alexandria, the last great mathematician of the Alexandrian School. The statement of this theorem, when properly stated, consists only of nine point and nine lines and we consider it one of the first great theorems of projective geometry. This thesis focuses on proofs of Pappus’s Theorem with intention of giving variety of methods and discussing differences between them while also presenting his generalizations and variations. In this thesis, we will emphasize special properties of this theorem which attains its full generality in projective geometry. We will state one of his Euclidean versions which is actually the specialization of the Pappus’s theorem when Pappus’s line is send to infinity. Pappus originally proved this theorem using Euclidean methods but in this thesis we will also describe two projective ways how to prove it using homogeneous coordinates. We will also present three variations of Pappus’s Theorem: Pascal’s Theorem, ChayleyBacharach-Chasles Theorem and Miquel’s Theorem. We will state and prove each of these theorems and explain what connections do they have with Pappus’s Theorem. We will end this thesis with algebraic proof of Pappus’s Theorem in its full generality by expressing the statements of Pappus’s Theorem using cross-products and a determinant. At first that proof seems to be very simple but the help of the computer program is essential here.