We know a lot about the world and our place in it. We have come to this knowledge in a variety of ways. And one central way that we, both as individuals and as a society, have come to know what we do is through communication with others. Much of what we know, we know on the basis of testimony.In Knowledge on Trust, Paul Faulkner presents an epistemological theory of testimony, or a theory that explains how it is that we acquire knowledge and warranted belief from testimony. The key questions addressed in this book are: what makes it reasonable to accept a piece of testimony? And what warrants belief formed on this testimonial basis? Faulkner argues that existing theories of testimony largely fail because they do not recognise how issues of practical rationalitymotivate the first question, and this is what makes testimony distinctive as a source of knowledge. At the heart of the theory this book presents is the idea that trust is central to answering these two questions. An attitude of trust can make it reasonable to depend on another's testimony, but whatwarrants testimonial belief is not trust but the body of evidence the testimony originates from. Testimonial knowledge and testimonially warranted belief are formed on trust. Faulkner goes on to argue that our having a way of life wherein testimony can provide such a source of knowledge and warrantis dependent upon a society in which a certain kind of trust is possible.