This book is devoted to a rapidly developing area of research known as the qualitative theory of dynamic equations. In the last 50 years the Oscillation Theory of ordinary, functional, neutral, partial and impulsive differential equations, and their discrete versions has attracted many researchers. However, most of these books on the subject only appeal to researchers who already know the subject. This in an effort to bring the subject to a wider audience, in this book the authors present a compact, but thorough, understanding of Oscillation Theory for second order differential equations. An important feature of this book is that the authors include several examples throughout the text, which not only illustrate the theory, but also provide motivation for new direction.