Objective: To review the treatment options for obsessive–compulsive dis-order (OCD), with particular reference to treatment resistance, and provide a guideline for clinicians managing these patients, drawing upon evidence from clinical trials and expert consensus. Conclusions: The behavioural technique of exposure and ritual pre-vention (EX/RP) and serotonergic medications have emerged as effective standard treatments of OCD, although full symptom remission is rare. Predictors of poor and partial response to these treatments may reflect sub-stantial underlying heterogeneity in OCD. Clinicians can now begin to apply psychological and pharmacological augmenting strategies that specifically target these heterogenous subgroups in an attempt to improve response. We offer a treatment algorithm for OCD derived from this under-standing.