Pervasive Developmental Disorders (PDDs) are a group of neurodevelopmental disorders characterized by significant impairments in social interaction, communication, and patterns of behavior, interests, and activities. These disorders typically appear in early childhood, usually before the age of three years, and affect multiple areas of development. The term Pervasive Developmental Disorders was used in earlier diagnostic systems such as the DSM-IV. In the DSM-5, most of these conditions are now included under the broader category of Autism Spectrum Disorder (ASD), except Rett Syndrome, which has a distinct genetic basis. Understanding PDDs is important in the field of mental health because they influence emotional, cognitive, behavioral, and social functioning throughout life. The major types of Pervasive Developmental Disorders include Autistic Disorder, Asperger's Disorder, Childhood Disintegrative Disorder, Rett Syndrome, and Pervasive Developmental Disorder-Not Otherwise Specified (PDD-NOS). Autistic Disorder is the most recognized form of PDD. It is characterized by marked deficits in reciprocal social interaction, delayed or absent language development, and repetitive or stereotyped patterns of behavior. Children may avoid eye contact, show limited interest in social relationships, and have difficulty understanding emotions and social cues. Many exhibit repetitive movements such as hand-flapping, rocking, or insistence on routines. Intellectual functioning varies widely, ranging from severe intellectual disability to above-average intelligence. Asperger's Disorder is characterized by significant difficulties in social interaction and restricted interests without marked delays in language or cognitive development. Individuals often possess average or above-average intelligence but struggle with understanding non-verbal communication, maintaining friendships, and adapting to social