 Historically, the distinction between knowledge by acquaintance and knowledge by description is made between two kinds of knowledge. However, after a brief discussion of Russell’s presentation of the distinction, we follow the contemporary literature in focusing more on the role of acquaintance in securing justified or rational belief. (See the entry on  epistemology  for more on the relation between knowledge and justification.) This is important both because doing so can illuminate the role that acquaintance plays in securing knowledge (which arguably requires justified belief) and because we may be interested in its role as a source of justification even when we fall short of knowledge. Let us say that one has an inferentially justified belief that p when one’s belief that p depends for its justification on justified belief in some other proposition(s) from which one can legitimately infer p; and one has a foundationally or noninferentially justified belief that p when one’s belief that p is justified but does not depend on any other beliefs for its justification. According to foundationalism regarding justification, we have some foundationally justified beliefs, and all other justified beliefs must depend for their justification on foundationally justified beliefs. Classical versions of foundationalism about justification hold that foundational beliefs are justified by acquaintance. (See the entry on  foundationalist theories of epistemic justification  for more on foundationalism.) As we shall see, proponents of classical foundationalism typically ascribe other important philosophical roles to acquaintance.