This book develops and defends a new externalist, reliabilist theory of knowledge and evidence, and develops a new view about scientific realism. Knowledge is viewed as a tracking theory that has a conditional probability rather than counterfactual formulation, and the property of closure under known implication is imposed on knowledge. It is argued that the tracking theory of evidence is best formulated and defended as a confirmation theory based on the Likelihood Ratio. These tracking theories of knowledge and evidence fit together to provide a deep explanation of why having better evidence makes one more likely to know. The new tracking theory of knowledge is argued to be superior to all currently known externalist rivals. It provides a distinctive explanation of why knowledge is more valuable than mere true belief, and explains why knowledge is power in the Baconian sense. Finally, the book argues that confirmation theory is relevant to debates about scientific realism, and defends a position intermediate between realism and anti-realism based on a view about what having evidence requires.