For many years essentialism - the view that some objects have essentially or necessarily certain properties without which they could not exist or be the things they are - was considered to be beyond the pale in philosophy, a relic of discredited Aristotelianism. This is no longer so. Kripke and Putnam have made belief in essential natures once more respectable. Harre and Madden have boldly argued against Hume’s theory of causation, and developed an alternative theory based on the assumption that there are genuine causal powers in nature. Dretske, Tooley, Armstrong, Swoyer and Carroll have all developed strong alternatives to Hume’s theory of the laws of nature. Shoemaker has developed a thoroughly non-Humean theory of properties. The new essentialism has evolved from these beginnings and can now reasonably claim to be a metaphysic for a modern scientific understanding of the world - one that challenges the conception of the world as comprising passive entities whose interactions are to be explained by appeal to contingent laws of nature externally imposed. In this volume Brian Ellis, who is seeking to develop the new essentialism, presents a general summation of the theory. It is designed to introduce students and generalists to an emerging metaphysical perspective that provides a comprehensive new philosophy of nature.