This chapter examines the modal dimension—the realm of what is possible and necessary—and some of its key metaphysical aspects. It begins by addressing Quine’s skepticism about modality, which posits that our attributions of modal properties to individuals, if meaningful at all, are always relative to a particular way of describing those individuals. This perspective aligns with a linguistic conception of modality, where what is possible or necessary is determined by the features of our language. In contrast, contemporary metaphysics often treats certain forms of modality as intrinsic features of reality. According to this metaphysical view, some possibilities and necessities are objective, that is, they are independent of linguistic or conceptual frameworks. This conception gained prominence with the introduction of the notion of possible worlds into philosophical discourse. Under this framework, what is necessary is true in every possible world, while what is possible is true in at least one possible world. The chapter explores two forms of realism about possible worlds. The first, a robust form defended by Lewis, posits that possible worlds are literally concrete entities. The second, a more moderate form of realism advocated by Plantinga, conceptualizes possible worlds as abstract entities.