Teachers regularly pose questions to their students, but the purpose and form of these questions can vary widely. This book is about a particular kind of question—one the authors call "essential." So, what makes a question "essential"? An essential question is open-ended, thought-provoking, calls for higher order thinking, points toward important, transferable ideas, raises additional questions, requires support and justification, and recurs over time. These are questions that are not answerable with finality in a single lesson or a brief sentence—and that's the point. Their aim is to stimulate thought, to provoke inquiry, and to spark more questions, including thoughtful student questions, not just pat answers. They are provocative and generative. By tackling such questions, learners are engaged in uncovering the depth and richness of a topic that might otherwise be obscured by simply covering it.