Bipolar disorder (BD) is a long-term illness with mood swings which are characterized by recurrent episodes of mania/hypomania and depression, with variable interpolations of relatively asymptomatic periods, called euthymic, in which, however, some psychopathological symptoms may persist. Although mood stabilizers, such as lithium, are the first-line treatment for the prevention of new BD episodes, combination therapy has become the standard of care for BD patients. Besides lithium, the use of a mood stabilizer along with an atypical antipsychotic is recommended in many patients. Recently, atypical antipsychotics (quetiapine, olanzapine, risperidone and aripiprazole) and antiepileptic agents (valproate, lamotrigine and oxcarbazepine) are increasingly used as mood stabilizers. To reduce side effects and optimize treatment it is important to perform accurate monitoring of drug blood levels in these patients, who are often treated with multiple drugs. Therapeutic drug monitoring (TDM) is in fact a powerful tool that, starting from clinical-chemical correlation data, allows to tailor-cut treatment to the specific needs of individual patients; hence the need to have reliable analytical methods available for the determination of plasma levels of drugs and their metabolites. Analyses of biological samples are mainly carried out using high-performance liquid chromatography (HPLC) coupled with different detectors, capillary electrophoresis and gas-chromatography. Various procedures are employed to remove biological interferences before analyzing the samples. This review focuses on currently available analytical TDM methods for atypical antipsychotics and antiepileptic agents used in the treatment of patients with bipolar disorder. Advantages and limitations of the various analytical methods will be reviewed and discussed, together with an evaluation of the role of TDM.