This paper aims to build a bridge between two areas of philosophical research, the structure of kinds and metaphysical modality. Our central thesis is that kinds typically involve super-explanatory properties, and that these properties are therefore metaphysically essential to natural kinds. Philosophers of science who work on kinds tend to emphasize their complexity, and are generally resistant to any suggestion that they have “essences”. The complexities are real enough, but they should not be allowed to obscure the way that kinds (...) are typically unified by certain core properties. We shall show how this unifying role offers a natural account of why certain properties are metaphysically essential to kinds. (shrink)