What is the relationship between ontology and modality: between what there is, and what there could be, must be, or might have been? Throughout a distinguished career, Bob Hale’s work has addressed this question on a number of fronts, through the development of a Fregean approach to ontology, an essentialist theory of modality, and in his work on neo-logicism in the philosophy of mathematics. This collection of new essays engages with these themes in Hale’s work in order to make further progress in our understanding of ontology, modality, and the relations between them. Some essays directly address questions in modal metaphysics, drawing on ontological concerns. Others raise questions in modal epistemology and its links to matters of ontology, such as the challenge to give an epistemology of essence. There are also several essays engaging with questions of what might be called ‘modal ontology’: the study of whether and what things exist necessarily or contingently. Such issues can be raised and addressed directly, but they also have an important bearing on the kinds of semantic commitments engendered in logic and mathematics, e.g., to the existence of sets, or numbers, or properties, and so on. It is thus explored in some chapters to what extent one’s ontology—and indeed, one’s ontology of necessary beings—interacts with other plausible assumptions and commitments.