Worldwide, over 300 million people are affected by depression and approximately 264 million are affected by anxiety disorders. Cognitive behavioral therapy (CBT) is a treatment commonly used for these disorders, but does it help? We conducted a meta-analysis to discern how effective CBT is for anxiety and depression. To do so, we collected 18 articles from PsycINFO; we found that most effect sizes were either medium or large, indicating that CBT is an effective treatment for anxiety and depression. Additionally, CBT works best under certain conditions: treating depression (d = 1.09), 10-15 year olds (d = 1.17), in person (d = 1.02), individually (d = 1.03), and in a therapy/outpatient setting (d = 1.05). These results suggest that CBT’s effectiveness varies due to many factors, but it is an effective method for treating anxiety and depression.