Theory-of-mind research has been carried out for over three decades, examining the ways children understand the minds of others--their perspectives, intentions, desires, and knowledge. Since the early 21st century, theory-of-mind studies have begun exploring the ways in which children think and reason about the minds--not only of ordinary, visible figures such as humans or animals--but of invisible figures such as spirits, angels, imaginary friends, and God. This growing body of research provides insight into children's cognitive development generally, but also into what could be called a "theory of religious mind."