The theory of mind (ToM) refers to how people understand their own thoughts and feelings and those of other beings. It is a crucial cognitive mechanism for social interactions and communication. It helps us to predict, to explain, and to manipulate behaviors or mental states. Moreover, this skill is shared by almost all human beings beyond early childhood. The literature presents different explicit false-belief tasks as a means of investigating ToM in children (e.g., one of the most famous is known as the Sally-Anne task). Although children younger than 4 years usually fail in these explicit tasks, it cannot be excluded that some less complex forms of understanding mental states develop earlier. So, in order to investigate the precursors that anticipate the emergence of a more mature representational system, many recent studies on infants’ beliefs have demonstrated, in the last decade, a very early sensitivity specifically to the false beliefs of others by using implicit looking-time tasks. This entry starts with the definition of the theory of mind and its history, before moving on to summarize developmental research in this area. Finally, it focuses on the relation between theory of mind and the possible with some reflections on how an increasing consciousness of the variety of situations that the possible presents to us could allow people to choose the best alternative for themselves and others.