During the coronavirus disease 2019 (COVID-19) pandemic, all European countries were hit, but mortality rates were heterogenous, with some countries being hit very hard, while others including Greece had a much lower death rate during the first wave of spring 2020. The ultra-fast application of measures was probably the reason of this outstanding success. This outbreak is expected to trigger feelings of fear, worry, and stress, as responses to an extreme threat for the community and the individual. In addition, changes in social behavior, as well as in working conditions, daily habits and routine, are expected to impose further stress, especially with the expectation of an upcoming economic crisis and possible unemployment. In Greece, where the lockdown was extremely successful in terms of containing the outbreak, worries concerning the possible adverse effects on mental health were also predominant. A collaboration concerning mental health during the COVID-19 outbreak was established, between the Aristotle University School of Medicine, the Panhellenic Medical Association and the World Psychiatric Association. Two large multinational studies were launched, one concerning the general population and one university students. Students' mental health is an area of special interest, both because of the vulnerability of this age group as well as because any disruption during the time of the studies has profound long-term consequences in the lives of the individuals, and this might trigger feelings of fear, worry, and stress. According the results from the Greek arm of the students' study, during the lockdown, two-thirds of university students reported at least 'much' increase in anxiety, one third in depressive feelings and in 2.59% concerning suicidal thoughts. There was also a worsening of quality of life and deterioration of lifestyle issues. Major depression was present in 12.43% with an additional 13.46% experiencing severe distress. Beliefs in conspiracy theories enjoyed wide acceptance ranging from 20-68%, with students of law, literature, pedagogics, political sciences and related studies manifesting higher acceptance rates. Female sex and depression/dysphoria both independently but also in interaction were related to higher rates of such beliefs. The results of the Greek arm of the general population study suggested that during the lockdown, clinical depression was present in 9.31%, with an additional 8.5% experiencing severe distress. Increased anxious and depressive emotions (including subclinical cases) were present in more than 40% of the population. In persons with a previous history of depression, 23.31% experienced depression vs. 8.96% of cases without previous history, who were experiencing their first depressive episode. Family dynamics suggested that fewer conflicts and better quality of relationships were surprisingly related to higher anxiety and depressive emotions, higher rates of depression and distress, and greater rates of suicidal thoughts. Eventually, spiritual and religious affiliation could protect the individual from the emerging suicidal thoughts. As correlation does not imply causation, the results suggest that conspiracy theories could be either the cause of depression or on the contrary a coping mechanism against depression. After taking into consideration that also in the family environment the expression of anger seemed to be a protective factor, the most likely explanation could be that the beliefs in conspiracy theories are a coping and 'protective' mechanism against the emergence of depression. These studies were among the first published, they went deeper in the data collection and even led to the creation of a model with distinct stages for the development of mental disorders during the lockdown. The analysis of the international data will probably provide further insight into the prevalence of mental disorders and the universal but also culturally specific models and factors pertaining to their development. At the time this editorial was in press, more than 40 countries representing more than two thirds of earth's population were participating with more than 45,000 responses already gathered.