 It is one of the tasks of a philosophical theory of modality to give a systematic and unified account of this multiplicity of modal concepts. This article discusses a few of the main issues that need to be addressed by anyone pursuing this goal. Sections 1 and 2 concern the question of what fundamental categories of modal notions there are. The focus will be on two contemporary debates: whether there are separate forms of modality that are tied to the epistemic and the metaphysical domains (section 1), and whether there is a special kind of necessity associated with the laws of nature (section 2). Section 3 discusses questions about the relations between different notions of necessity. Can some of them be reduced to other, more fundamental ones? If so, which concepts of necessity are the most fundamental ones? And if there are several fundamental kinds of necessity, what do they have in common that makes them all kinds of necessity?