Beliefs are central for understanding knowledge and justification, pervasive in explaining human conduct, and the major constituents of our conceptions of reality. This chapter will describe belief in an overall way, but its main concern is to clarify and bring out the significance of different forms of believing. When these are accounted for, we can better understand the kinds of content beliefs have, how that content is connected with reference, and how perception plays an essential role in both our formation of beliefs and their constituting knowledge when they do so. I begin with some basic points about the nature and forms of belief. Against that background, I explore when belief content is internal rather than external, provide a sketch of a theory of internal content, and conclude with some implications for the theory of justification.