In this groundbreaking new book, Manuel Delanda analyzes all the different genres of simulation (from cellular automata and genetic algorithms to neural nets and multi-agent systems) as a means to conceptualize the possibility spaces associated with causal (and other) capacities. Simulations allow us to stage actual interactions among a population of agents and to observe the emergent wholes that result from those interactions. Simulations have become as important as mathematical models in theoretical science.