This chapter examines the role of the endocannabinoid (eCB) system in psychiatric disorders, including anxiety, depression, eating disorders, post-traumatic stress disorder (PTSD), substance use disorders (SUDs), autism spectrum disorder (ASD), and schizophrenia. We begin with an overview of the eCB system’s key functions in regulating stress, fear, emotional processing, metabolism, and synaptic plasticity. Dysregulation of this system has been linked to various psychiatric conditions. In anxiety and depression, for example, disruptions in eCB signaling influence both emotional regulation and stress response, with pharmacological interventions targeting eCB pathways showing promise in preclinical models. In SUDs, altered eCB functioning, particularly involving FAAH and AEA, has been linked to addiction-related behaviors, though human clinical findings remain mixed. In ASD, preclinical studies suggest that eCB signaling influences social behaviors, with FAAH inhibitors showing potential in reversing ASD-like social deficits. However, clinical trials on eCB-targeted therapies for ASD have yet to show significant effects. In schizophrenia, elevated AEA levels have been observed, but the role of specific genetic variations in the FAAH gene remains unclear. We conclude by calling for further research on gene-environment interactions and longitudinal studies to deepen understanding of eCB signaling in psychiatric risk and potential therapies.