Abstract: Introduction: This narrative review sets out to explore the current literature surrounding the mental health of serving personnel and veterans. Sources of data: UK literature published in peer-reviewed scientific journals and publicly available UK Ministry of Defence reports. Areas of agreement: Evidence suggests that common mental disorders are more prevalent in the UK serving and veteran personnel than in the general population. Risk factors include being female, adverse childhood events, combat exposure, and physical combat injury. Areas of controversy: Post-traumatic stress disorder rates are broadly similar between UK serving personnel and the general population, though certain groups are at increased risk, such as veterans who deployed to Iraq/Afghanistan in combat roles. Growing points: Understanding ways to maximize positive psychological outcomes, address poor sleep, and support those with combat injuries and chronic pain are key priorities for research/interventions. The prevalence of moral injury and military sexual trauma in the UK Armed Forces is currently unknown. Areas timely for developing research: A longitudinal study following recruits including those who are part of the Lesbian, Gay, Bisexual, Transgender, Queer/Questioning or other sexualities and gender identities (LGBTQ+) community, or who have a neurodivergent condition, from entry to post-service would enhance our understanding of how serving in the Armed Forces impacts the mental health and wellbeing.