This book deals with the main proponents of the causal and descriptivist reference theories on natural kind terms. The two main types of contemporary reference theories on natural kind terms are the causal and the descriptivist theories. The author analyzes the main versions of these two types of theories and claims that the differences between them are not as great as it is usually assumed. He alleges that the ostensive reference fixing and reference borrowing theories should be descriptive-causal, and he also adduces that the relation of kind-identity depends on the views on kind-identity and thus involves descriptive elements. This book is an important contribution to the debate on reference in contemporary philosophy of language and linguistics.