 This entry is organized as follows. In section 1 (The Origins and Varieties of ST), we briefly reconstruct ST’s history and elaborate further on ST’s main theoretical aims. We then go on to explain the very idea of mental simulation (section 2: What is Meant by “Mental Simulation”?) In section 3 (Two Types of Simulation Processes), we consider the cognitive architecture underlying mental simulation and introduce the distinction between high-level and low-level simulation processes. In section 4 (The Role of Mental Simulation in Mindreading), we discuss what role mental simulation is supposed to play in mindreading, according to ST. This discussion carries over to section 5 (Simulation Theory and Theory-Theory), where we contrast the accounts of mindreading given by ST and TT. Finally, section 6 (Simulation Theory: Pros and Cons) examines some of the main arguments in favour of and against ST as theory of mindreading.