The current chapter provides a comprehensive overview of the molecular aspect underlying the pathogenesis of ASD. Transcriptomic studies, employing techniques such as microarray analysis, RNA sequencing (RNA-Seq), and single-cell RNA-Seq, have revealed regional and cell type-specific alterations in gene expression profiles in the brains of individuals with ASD. These studies have identified differentially expressed genes (DEGs), alternative splicing events, and dysregulated pathways associated with ASD, shedding light on the molecular mechanisms underlying the disorder. Key findings include dysregulation of genes involved in ASD, neuronal signaling, and immune response across various brain regions. Genetic and environmental factors contribute to transcriptomic alterations observed in ASD, with rare and common genetic variants, as well as prenatal exposures, influencing gene expression patterns in the developing brain. Challenges in the field include sample heterogeneity, limited sample sizes, postmortem tissue quality, and technical variability, which necessitate future studies leveraging larger sample cohorts, multi-omics data integration, and advanced analytical techniques. Therapeutic implications of transcriptomic findings include the identification of potential therapeutic targets and candidate biomarkers for ASD diagnosis and treatment, with targeted interventions aimed at modulating dysregulated pathways holding promise for improving outcomes in individuals with ASD.