The qualitative theory of dynamic equations is a rapidly developing area of research. In the last 50 years, many scholars have studied the oscillation theory of ordinary, functional, neutral, partial, and impulsive differential equations. Many books deal with oscillation theory, but in a way that appeals only to researchers already familiar with the subject. In an effort to bring the topic to a new and broader audience, the authors clearly explain oscillation theory for second-order differential equations. They include several examples to illustrate the theory and to inspire new direction. This text is ideal for students and researchers in applied mathematics, engineering science, and numerical analysis.