The concept of mood stability is attractive to both patients and clinicians alike, and hence the term ‘mood stabilizer’ has widespread currency. However, its worldwide acceptance and use in clinical practice is at odds with the absence of official recognition by regulatory authorities. The ideal mood stabilizer is said to have efficacy in the treatment of acute manic and depressive episodes, and also be effective in the prevention of recurrences. However, in reality, few drugs with perhaps the exception of lithium, come close to this gold standard; yet many agents aspire to the title, and some have arguably achieved it prematurely. It is, therefore, important to reconsider the definition of a mood stabilizer and critically review which agents, if any, satisfy the necessary eligibility requirements by reference to reasonable criteria and comparator data. The term mood stabilizer is an important label. It needs to be applied judiciously because it confers clinical credibility and qualifies long-term use in maintenance and prophylaxis. It is also important with respect to developing guidelines for treatment and the further development of novel agents. Most importantly, however, it is a term that is innately appealing because of what it promises: for this reason alone it should encompass only those agents that can deliver.