This chapter introduces the main issues and themes of the volume. Approaches to individuality from metaphysics and philosophy of science are contrasted. Recent philosophical developments regarding concepts of biological and physical individuality are exposed. These research trends show how philosophy of physics and philosophy of biology address differently the question of what an individual is. Five main divergences are identified: the centrality of part-whole questions, the issue of identical individuals, the importance of the Principle of the Identity of Indiscernibles and, (...) finally, the importance of structuralist concerns. At the end of the chapter, the structure of the book is explained in detail. (shrink)