Use of augmenting agents in schizophrenia is a common practice in response to resistant symptoms or comorbid illness. Increasingly, clinicians are combining more than one antipsychotic agent, despite a lack of evidence from controlled studies to support this approach. A rationale can be made for adding higher-potency agents to clozapine in an attempt to optimize D2 dopamine receptor blockade, but this strategy requires further study before it should be adopted in clinical practice. Older reports have explored the use of antidepressants, mood stabilizers, and anxiolytics as augmenting agents. These agents appear to improve comorbid affective or anxiety symptoms, but earlier evidence of improvement in psychotic or negative symptoms has not been replicated consistently. Glutamatergic agents acting at the glycine coagonist site of the N-methyl-D-aspartate receptor, including glycine, D-cycloserine, and D-serine, have demonstrated impressive therapeutic effects for negative symptoms when added to conventional neuroleptic agents, but do not appear to enhance clozapine efficacy. Given the high rates of symptom persistence and disability associated with schizophrenia, the need for augmentation strategies is great, but no approach has clearly emerged as effective for a substantial portion of patients. Although certain approaches may prove helpful for individual patients, augmentation should not be used unless monotherapy has been optimized, and should not be continued long-term unless benefits are clear.