Inclusion Criteria:

• Diagnosis: Major depression, unipolar without psychotic features (by DSM-IV criteria) -Severity of depression: A 24-Item HDRS above 19 at screening and at baseline -
• Level of Executive Dysfunction: Two strata within each age stratum: Stroop Color-Word scores - one half of the sample < 26, one of half ≥ 26.
• Capacity to provide informed consent.

Exclusion Criteria:

• High suicide risk, i.e. intent or plan to attempt suicide in near future
• Presence of any current Axis I psychiatric disorder (other than unipolar major depression or specific phobias) including substance abuse (those with a history of substance abuse must be abstinent for at least 3 months prior to entry)
• Axis II diagnosis of antisocial personality disorder, mental retardation and pervasive developmental disorder (DSM-IV)
• History of psychiatric disorders such as psychotic depression, primary psychotic disorder, or bipolar spectrum disorder (bipolar disorder, hypomania, and dysthymia are exclusions)
• Cognition: MMSE scores below 24 or diagnosis of dementia by DSM-IV
• Acute or severe medical illness, i.e., delirium, metastatic cancer, decompensated cardiac, liver or kidney failure, major surgery, stroke or myocardial infarction during the three months prior to entry; or drugs known to cause depression, e.g., reserpine, alpha-methyl-dopa, steroids, sympathomimetics withdrawal
• Presence of a significant neurological disease such as Parkinson's disease, primary or secondary seizure disorders, intracranial tumors, severe head trauma; neurodegenerative diseases i.e. MS
• History of electroconvulsive therapy
• History of failure to respond to escitalopram (Lexapro) (20mg/day for 6 weeks or longer) during the current or previous depressive episodes
• Current psychotherapy
• History of intolerance to escitalopram (Lexapro) or use of concomitant drugs that may provide reason to believe that escitalopram is contraindicated.

Active treatment with fluoxetine at the time of screening

• Patients' unwillingness or inability to gradually withdraw all other psychotropic medications (except for the following: Low and stable doses of opiates and non-benzodiazepine hypnotics (e.g. zolpidem (5 or 10 mg), zaleplon (5 or 10 mg), or eszopiclone (1 or 2 mg).Low and stable doses of diazepam and other anxiolytics should be tapered at screening; inability to tolerate taper is not an exclusion criteria.
• Inability to perform any of the ADLs (MAI: ADL subscale) even with assistance, e.g. walking with a cane is not an exclusion criterion
• Inability to speak English
• Aphasia