Autism Spectrum Disorder (ASD) is a complex neurodevelopmental disorder characterized by social-communication and interaction deficits and restricted, repetitive patterns of interests and behavior. It is frequently associated with heterogeneous comorbidities including physical, mental, and neurodevelopmental disorders, which can result in a substantial burden on individuals, families, and society. Early prodromal signs of ASD emerge during the first year of life, a time when brain plasticity is at its maximum level, and may consist of diminished social orienting, responsivity and reciprocity combined with the presence of prolonged visual fixation and repetitive use of objects. Developmental immaturities in communication and motor skills are often present too. Pre-emptive Intervention (PI) for infants with prodromal signs of ASD was shown to improve outcomes, in comparison to later starts, by improving developmental skills, reducing ASD symptoms and, in some cases, preventing the full blown symptoms of ASD. Moreover, access to early evidence-based interventions may reduce the elevated levels of stress, anxiety and depressive symptoms experienced by caregivers of children with signs of ASD. Despite this evidence, professionals tend to have a 'wait to see' approach, rather than targeting areas of impairment with early intervention. Moreover, the vast majority of current clinical models of ASD services require a diagnosis to receive services, while the identification of prodromal signs of the disorders generally is not sufficient to access early intervention. There is an urgent need for a paradigm shift in ASD treatment. Our proposed Project aims to evaluate the efficacy of FIRRST, a parent-mediated PI for infants with early signs of ASD. We will conduct a multisite RCT of telehealth PI by recruiting 132 symptomatic infants between 9-14 months and randomly assigning them to receive either FIRSST (experimental group), or Parent Education (control group). Developmental skills, ASD symptomatology, caregiver well-being and brain changes on High-Density EEG will be assessed with in-presence evaluations at three time points: 1. baseline; 2. after 24 weeks of intervention; 3. follow-up after 24 weeks from the end of intervention. If funded, our study will be the first well-powered RCT evaluating developmental, symptom and neurophysiological changes in response to a parent-mediated PI conducted in Europe. The ultimate goal for translational research in ASD lies in the optimization of clinical outcomes through the most effective, targeted, and timely treatments. Our proposed RCT has the potential to significantly impact current access to services by reducing the age of starting intervention, thereby promoting optimal developmental outcomes, as well as reducing burden and high health costs to families and society.