This book concerns the role others play in our attempts to acquire knowledge of the world. Two main forms of this reliance are examined: testimony cases, where a subject aims to acquire knowledge through accepting what another tells her; and cases involving "coverage," where a subject aims to acquire knowledge of something by reasoning that if things were not so she would have heard about it by now. It is argued that these cases challenge some cherished assumptions in epistemology. Testimony cases challenge the assumption, prominent in reliabilist epistemology, that the processes through which beliefs are formed never extend beyond the boundaries of the individual believer. And both sorts of case challenge the idea that, insofar knowledge is a cognitive achievement, it is an achievement that belongs to the knowing subject herself. The book uses results of this sort to question the broadly individualistic orthodoxy within reliabilist epistemology, and to explore what a non-orthodox reliabilist epistemology would look like. The resulting theory is a social-reliabilist epistemology -- one that results from the application of reliabilist criteria to situations in which belief-fixation involves epistemic reliance on others.