The aim of writing the paragraph is to provide a broad understanding of depression, which is a common word for nowadays teens but people seldom really understand it. This essay first introduces various types of depression, then provide information about causes that leads to depression, including genetics and biology, brain chemistry imbalance, poor nutrition, female sex hormones, stress and trauma, substance use, physical health condition and also seasonal changes. Besides, different treatments for depression are listed. For example, psychotherapy, medications or change of lifestyle. It provides a complicated map of depression. However, there are still areas left to be discovered, hope the key brain pathways for causing depression will provide more explanation about the cause of depression.