This chapter is a critical introduction to different (classical and non-classical) semantics for deontic modals, in particular semantics given to ‘ought’. After some methodological considerations on the role of semantic and philosophical inquiry on modality and natural language modality (Sect. 1.1), I briefly consider what is now considered the classical semantic proposal for (deontic) modals, as given mainly by Angelika Kratzer from the 70s onwards (Sect. 1.2), which under minor assumptions is proved equivalent to the possible world semantics for standard deontic logic. In particular, I consider extensions of the standard semantic proposal to account for features such as strong versus weak necessary modals.