Depression, or major depressive disorder, is a mood disorder characterized by sadness, inactivity, mental instability, and feeling of hopelessness. It has a severe effect on the mental and social health of adolescents. The purpose of this research is to explore the problems that cause adolescents to develop depression. Common causes of depression discovered in this research include family factors, social factors, and gender differences. Depression can be a genetically predisposed condition. Maternal depression is most commonly associated with depressive cognitions and adolescent depression. By observing negative behavior, from a depressed parent, an adolescent can develop depressive cognitions also. Bullying is a social factor that can cause an adolescent to fall into depression. Both bullies and victims are at an increased risk for depression when bullying frequently occurs. Cyber-bullying, a relatively new form of bullying, uses technology to publicly humiliate innocent victims and has the highest rate of depression among bullying victims. When adolescents commit delinquent acts, they are also prone to developing the disorder. Committing a single delinquent act is enough to lead an adolescent to depression. Incarceration can also cause depression or increase the severity of a current depressive episode. Depression may be a consequence for young adolescents involved in romantic relationships. Young females engaged in a romantic relationship with an older partner are at the highest risk for developing depression. Stressful life events such as a death in the family, abuse, and traumatic experiences are another cause of adolescent depression. Adolescents who believe they are at fault for an event are at the highest risk for depressive disorder. Gender differences, also known as puberty, may determine if an adolescent develops depression. Females are at a higher risk for developing depression during puberty than males.