Patients with schizophrenia are characterized by a broad range of neurocognitive abnormalities. These include impairments in attention, including abnormalities in sensory gating; executive function; visual and verbal learning and memory; working memory; processing speed; and social cognition (Nuechterlein et al, 2004). These impairments are major determinants of poor functional outcome in patients with schizophrenia (Green, 1996; Green et al, 2004). Conventional antipsychotics have limited effects on these impairments. Second generation antipsychotics may have modest benefits for cognitive function, but whether this represents a direct cognitive enhancing effect has not been established. Regardless, patients continue to exhibit pronounced cognitive impairments despite adequate second generation antipsychotic treatment. Adjunctive pharmacotherapy may offer a viable approach for the treatment of cognitive impairments. Adjunctive agents can be used to modulate specific neurotransmitter systems that are hypothesized to be involved in the pharmacology of cognitive functions.