Skeptics have cast doubt on the idea that scientific theories give us a true picture of an objective world. Lawrence Sklar examines three kinds of skeptical arguments about scientific truth, and explores the important role that these play within foundational science itself, especially physics. First, doubts have been expressed about the legitimacy of claiming truth for assertions about the realm of the unobservable. Second, scientific theories have been characterized as relying heavily on idealization of the physical systems they seek to describe. Third, it is noted that scientific theories tend to be transient, and even the best currently available are expected to be replaced in the future. Sklar demonstrates that these kinds of philosophical critique are employed within science itself, and reveals the clear difference between how they operate in a scientific and in a more abstract philosophical context. The underlying theme of Theory and Truth is that science and philosophy are essential to, and inextricable from, each other. One cannot understand the methods of science except by understanding philosophy, and one cannot fruitfully pursue philosophy of science without understanding foundational science as well. Theory and Truth is a revised version of the John Locke Lectures delivered by Professor Sklar at the University of Oxford in 1998.