Textbook in PDF format The focus of the present book is to give an introduction to each of the topics of sets and logics, graphs, relations, functions, combinatorics, and number theory. The topics of the book may be covered in a one semester course, taken in sequence from sets and logic through to number theory. The chapters may be read independently, although a grasp of Chapter 1 on sets and logic is important to everything that follows. The book contains 180 exercises ranging in difficulty from easier to more challenging. Solutions are included at the end of each chapter for almost all the exercises. In some cases, only hints towards the solutions are provided. There are dozens of examples and figures that will aid in the comprehension of the material