The identity of a natural kind can be construed in terms of its causal profile. This conception is more appropriate to science than two alternatives. The identity of a natural kind is not determined by one causal role because one natural kind can have many causal roles and several functions and because some functions are shared by different kinds. Furthermore, the microstructuralist thesis is wrong: The identity of certain natural kinds is not determined by their microstructure. It is true that if A and B have the same microstructural composition then a sample of a chemical substance A is of the same chemical substance as a sample of B. However, the reverse does not hold. It is not the case that if a sample of a chemical substance A is of the same chemical substance as a sample of B then A and B have the same microstructural composition. This is because a macroscopic NK can be "multiconstituted" by different microstructures.