Depression is one of the most common psychiatric complications of Alzheimer disease (AD), affecting from 30% to 50% of prevalence, with most estimates in the 20-30% range. Because of having a presentation in the context of AD that differs from typical early-onset depression, it is not easy one to detect and quantify reliably, and can be difficulty to differentiate depression from the other neuropsychiatric symptoms of AD. Due to the lack of large randomized trials, optimal treatment and the true degree of efficacy remains undetermined. However, these treatments can reduce adverse impact of depression on patients and caregivers. This article provides a practical discussion of the diagnosis, evaluation, differential diagnosis and treatment of depression in AD for the clinician.