This chapter describes the potentially novel role of platelets in neuropsychiatric disorders and describes their promising role as peripheral biomarkers and as treatment targets. In addition to their haemostatic activities, platelets, which share structural and functional features with neurons, are involved in neuroinflammation, modulation of neurotransmitters and maintenance of blood-brain barrier (BBB) integrity. Structural and functional abnormalities in platelet morphology and signalling that affect the release of neurotransmitters, calcium signalling and inflammatory mediators are observed in a variety of disorders including depression, schizophrenia, bipolar disorder, paediatric acute-onset neuropsychiatric syndrome (PANS), Tourette’s syndrome, autism spectrum disorders (ASD), anxiety disorders (AS) (e.g. generalised anxiety disorder [GAD], panic disorder [PD], post-traumatic stress disorder [PTSD]) and eating disorders (e.g. anorexia nervosa and bulimia nervosa). These changes promote systemic inflammation, oxidative stress and disruption of the BBB, suggesting mediation by the gut microbiota. The resulting chapter addresses the particular platelet abnormalities in each disorder, the clinical consequences of such platelet dysfunction and some potential therapeutic approaches involving SSRIs, anti-inflammatory agents, antioxidants, omega-3 fatty acids and physical exercise. By providing an integrative perspective on abnormal neurogenic markers of peripheral origin, targeted new approaches to diagnosing and monitoring the progression of neuropsychiatric disorders as well as more personalised treatment of these disorders may become possible.