This review article shows cross-sectional studies and longitudinal research papers dealing with the biological, psychological, and social factors contributing to the development and the persistency of depression, anxiety, and mixed anxiety-depression disorder. The objective of summarising these studies was to provide a detailed insight into the current understanding about the workings of biopshychosocial factors in relation to the previously mentioned disorders, to review the most relevant results, and to offer guidelines for future research. The studies have, for the most part, consistently shown that impairment in performing everyday activities, lacking social support, and cognitive impairments are all major risk factors for developing anxiety and depression. For the mixed anxiety-depression disorder, the results have failed to show the same level of consistency as they did for individual disorders, but the authors of those studies mostly agree that the mixed anxiety-depression disorder shows symptoms of depression and anxiety that are more noticable and exceeding in quantity and that the history of those symptoms are a good predictor for the development of MAD. Besides that, the researchers agree that there is less chance of recovering from MAD than of “pure” depression or anxiety and that it more often affects younger old population in comparison to very old population. Future research should investigate mentioned risk factors in more detail, especially among people over the age of 85 due to the lack of research on this topic. In addition, the purpose of this kind of research should be providing information for prevention of these disorders, as well as the development of appropriate treatments for them.