Depression among children and adolescents is linked to a variety of negative outcomes, but many causes of depression are either difficult or impossible to alter. It is vital to identify the controllable causes of depressive symptoms, including time spent on screen media. Many studies demonstrate associations between time spent on social media and depressive symptoms. Time-lag evidence also demonstrates an association, with rates of adolescent depression doubling during the period when smartphone and social media use became common. Experimental evidence indicates that cutting back on social media use diminishes depressive symptoms. Social media time may cause depressive symptoms via several mechanisms including displacing time spent on healthy activities, increased body image concerns, cyberbullying, reinforcing spirals of negative content, and interference with sleep. Future research should include experimental trials among adolescents, determine which types of screen activities and social media platforms are most strongly linked to depressive symptoms, explore which populations are most impacted, and determine effective interventions. Recommendations include educating parents and adolescents to keep devices out of their bedrooms overnight, not allowing children and younger teens to use social media, and encouraging parents to model appropriate limits around screen devices.