 Section 3 describes four main uses of CA in philosophical investigation. Firstly, since CA display complex behavioral patterns emerging from simple local rules, they have been naturally linked to emergence: this topic is dealt with in Section 3.1, where different notions of emergence are considered. Secondly, Section 3.2 explores how CA have been put to work, both by philosophers and by scientists, to address the traditional philosophical problems of free will and determinism. Thirdly, Section 3.3 describes the impact of CA theories on the philosophy of computation. Finally, Section 3.4 addresses ontological issues ranging from the sense in which CA count as modelling portions of reality, to the bold philosophical conjecture of some scientists, who claim that the physical world itself may be, at its bottom, a discrete, digital automaton. 