 The growth of philosophical interest in biology over the past forty years reflects the increasing prominence of the biological sciences in the same period. There is now an extensive literature on many different biological topics, and it would be impossible to summarise this body of work in this single entry. Instead, this entry sets out to explain what philosophy of biology is. Why does biology matter to philosophy and vice versa? A list of the entries in the encyclopedia which address specific topics in the philosophy of biology is provided at the end of the entry.