How can a single species of insect pose a threat to millions of acres of forests, orchards, and street trees? What can we do about the Asian longhorned beetle and other plants and animals that invade our farms, cities, and forests? The study of ecology helps us to find answers to these questions. Through applying ecological principles and conducting research, scientists are learning to manage invasive species. Students can learn alongside the scientists and, in some cases, help them. This chapter defines the term invasive species using a variety of examples—such as the Asian longhorned beetle and Chestnut Blight—and discusses their ecological implications. This free selection includes the Table of Contents and Preface.