In the field of Autism Spectrum Disorders (ASD), the importance of an early diagnosis is internationally recognized. Green and Red Bells stems from the need to actively and directly involve professionals and volunteers working in the field of early childhood in the early identification of those peculiar behaviours that could lead to a diagnosis of ASD. It is not a diagnostic tool, but an observation guide, which aims to facilitate communication with family members and professionals who will, if necessary, investigate the diagnostic aspect. The manual has the dual purpose of facilitating the observation of the child, by means of cards who can be easily administered, and helping to communicate what has been observed in an objective and effective manner, thanks to the attached summary sheet, which helps highlight any priorities in the following discussion. The choice of the observed behaviours was made after consulting several articles concerning the early signs of ASDs. In particular, the study by Dereu and colleagues (2010).