"Will It Fly?" is a book by Pat Flynn that helps entrepreneurs evaluate their business ideas. It provides a structured approach to testing concepts before investing time and money. The book emphasizes the importance of validating ideas through research and feedback from potential customers. In "Will It Fly?", Flynn introduces a simple framework called the Flywheel, which guides readers through the process of assessing their ideas. By focusing on key factors like market demand and personal passion, the book aims to increase the chances of success for new ventures.