By now we all know how important mental representations are for any goal-directed actions. But, if I have my mental representations and you have yours, can I improve my actions by having a representation of your representation? If I have such a representation, I am able to acknowledge that you are like me, in the sense that you have your own mental representations and goal-directed actions. This dialogue is referred to as the Theory of Mind because I have a “theory” (a model or representation) of your mind. In fact, I may even have a representation of your representation of my representations. These kinds of first-order and second-order representations are important in evaluating false beliefs and deception. The simpler types of reasoning are already present in preschool children, as illustrated in the first study described in this chapter. More complex types of reasoning show up later in development, so adults can use them. Forming representations of others’ representations happens in visual perception, as well, where it is called “visual perspective taking.” Children are capable of reasoning about what other people can or cannot see and they can make these visual inferences not only by looking at a 3D scene, but also by looking at pictures of 3D scenes. The second half of this chapter describes in some detail a systematic, quantitative study of a matrix game that has been used to examine levels of recursive resoning.