 Arthur has the measles and stays in a closed environment with his little sister Mafalda. If Mafalda ends up contracting the measles herself because of her staying in close contact with Arthur, there must be something—the measles virus—which is transmitted from Arthur to Mafalda in virtue of a relation—the relation of staying in close contact with one another—instantiated by the two siblings. Epistemologists have been devoting their attention to the fact that epistemicproperties—like being justified or being known—are often transmitted in a similar way. An example—which we shall not discuss in this entry—is the transmission of knowledge via testimony from an individual to another. A different but equally important phenomenon—which occupies centre stage in this entry—is the transmission of epistemic justification across an inference or argument from one proposition to another.  