It is not a coincidence that every red rose is coloured. No rose can be red without being coloured. A red rose is coloured in virtue of its being red, its being coloured is metaphysically explained by its being red. This is, at least in part, underwritten by what it is for the rose to be coloured, by the nature - or essence - of its being coloured. If this is right, then questions concerning possibility and necessity, questions concerning metaphysical explanation, and questions concerning essence are systematically connected. This book proposes a unified account of metaphysical modality, grounding, and essence. It develops a semantic way to model essences as localised necessities that rule out worlds as impossible and uses it to account for grounding and metaphysical modality.