Background: Smartphone applications for mental illnesses offer great potential, although the actual research base is still limited. Major depressive disorder and bipolar disorder are both common psychiatric illness for which smartphone application research has greatly expanded in the last two years. We review the literature on smartphone applications for major depressive and bipolar disoders in order to better understand the evidence base for their use, current research opportunities, and future clinical trends. Methods: We conducted an English language review of the literature, on November 1st 2014, for smartphone applications for major depressive and bipolar disorders. Inclusion criteria included studies featuring modern smartphones running native applications with outcome data related to major depressive or bipolar disorders. Studies were organized by use of active or passive data collection and focus on diagnostic or therapeutic interventions. Results: Our search identified 1065 studies. Ten studies on major depressive disorder and 4 on bipolar disorder were included. Nine out of 10 studies on depression related smartphone applications featured active data collection and all 4 studies on bipolar disorder featured passive data collection. Depression studies included both diagnostic and therapeutic smartphone applications, while bipolar disorder studies featured only diagnostics. No studies addressed physiological data. Conclusions: While the research base for smartphone applications is limited, it is still informative. Numerous opportunities for further research exist, especially in the use of passive data for, major depressive disorder, validating passive data to detect mania in bipolar disorder, and exploring the use of physiological data. As interest in smartphones for psychiatry and mental health continues to expand, it is important that the research base expands to fill these gaps and provide clinically useful results.