The PHQ-9, or Patient Health Questionnaire-9, is a widely used tool for screening and measuring the severity of depression. It consists of nine questions that assess symptoms experienced over the past two weeks, such as feelings of sadness, loss of interest, and changes in sleep or appetite. Each question is scored from 0 to 3, allowing healthcare providers to evaluate the patient's mental health status. This questionnaire is often used in clinical settings and research to help identify individuals who may need further evaluation or treatment for depression. The PHQ-9 is simple to administer and can be completed in a few minutes, making it a practical option for both patients and healthcare professionals.