Purpose of review There is increasing recognition that a minority of bereaved persons experiences persistent and disabling grief symptoms, also termed complicated grief. We review currently proposed criteria for complicated grief in the Diagnostic and Statistical Manual of Mental Disorders (DSM 5) and the International Statistical Classification of Diseases and Related Health Problems (ICD-11), highlight controversies with regard to establishing complicated grief as a psychiatric disorder, summarize recent complicated grief treatment research within a cognitive behavioral treatment framework, and establish a novel and systematic research agenda for complicated grief treatment. Recent findings Clinicians should be wary of overdiagnosis and misdiagnosis of complicated grief. Recent changes to definitions of complicated grief may threaten generalizability and clinical application of research findings. Universal treatment, treatment for at-risk groups and preventive complicated grief treatment appear ineffective. Although medication is often prescribed to bereaved persons, evidence for its effectiveness is equivocal. Face-to-face and internet-based cognitive behavioral therapy techniques appear most effective in targeting complicated grief. However, little is known about what, how, and for whom treatment works best. Summary In light of these findings, we recommend systematic investigation of: what works best in complicated grief treatment, by conducting well designed, stepped effectiveness trials and treatment component dismantling studies; how it works, by conducting investigations on therapeutic theories and examining mediators of therapeutic change; and for whom it works, by examining potential moderators of treatment effects.