Theory of mind, the cognitive capacity to infer others' mental states, is crucial for the development of social communication. The impairment of theory of mind may relate to autism spectrum disorder (ASD), which is characterized by profound difficulties in social interaction and communication. In the current article, I summarize recent updates in theory of mind research utilizing the spontaneous false belief test, which assesses participants' spontaneous tendency to attribute belief status to others. These studies reveal that young infants pass the spontaneous false belief test well before they can pass the same task when explicitly asked to answer. By contrast, high-functioning adults with ASD, who can easily pass the false belief task when explicitly asked to, do not show spontaneous false belief attribution. These findings suggest that the capacity for theory of mind develops much earlier than was previously thought, and the absence of spontaneous theory of mind may relate to impairment in social interaction and communication found in ASD.