This book presents work at the forefront of contemporary scholarly debate about the relevance of substantial metaphysical theories to science. It comprises a series of original papers engaging with issues currently at the centre of this debate and responds in particular to two recent books by Brian Ellis on scientific essentialism, especially on the necessity of laws of nature, the nature of natural kinds and the nature of scientific realism. The collection contains a new paper by Ellis himself, as well as commentary and criticism from prominent philosophers in the field. It concludes with a reply by Ellis to some of his critics.