Accurate assessment is critical for the effective treatment of depression. Depression assessment can begin even earlier, at the public health level, before the need for treatment has become manifest. This chapter provides an overview of more than 20 measures that may be used in the assessment and treatment of depression for adults. The measures are listed in alphabetical order and separated into two categories: clinician ratings and self‐report inventories. The chapter describes each instrument's format, psychometric properties, and utility for various purposes (e.g., screening, diagnosis, treatment monitoring). The majority of depression instruments measure diagnostic criteria or symptom severity. The chapter also discusses depression measures designed for child, adolescent, and geriatric populations. It provides a case example and discusses future directions in depression assessment. The future of the assessment of depression may largely be influenced by the new editions of the diagnostic and statistical manual of mental disorders (DSM‐V) and ICD‐11.