This book provides a critical assessment of Nick Bostrom's simulation argument. The argument states that at least one of these statements must be true:

[P1] Almost all civilizations will not reach a posthuman stage.

[P2] Almost all posthuman civilizations will have no interest in creating ancestor simulations.

[P3] We are almost definitely living in a computer simulation.

I examine the soundness of Bostrom's argument by questioning some of his premises. I then propose a few modifications that address the issues raised. Thereafter, I suggest that Bostrom is wrong to assign equal credence to each outcome. Instead, I argue that outcome [P1] should be given preference because it requires the least amount of speculation and additional assumptions.

Section 1 introduces key concepts and explains why the Simulation Argument is worth our philosophical attention. Section 2 evaluates the two key assumptions underlying Bostrom's argument. Section 3 presents a formal mathematical exposition of the Simulation Argument. This section also discusses several problems with the argument and suggests how they can be overcome. Section 4 looks at each of the three outcomes and discusses how we should best interpret them. I conclude by agreeing with Bostrom that the simulation hypothesis, however unlikely, is fundamentally different from other well-known scepticism scenarios.