Several percent of a population are affected by mental disorders: 1 % has schizophrenia, 2 % are alcohol addicted and about 10 % have depression. Family studies, twin studies and adoption studies showed that there is a strong genetic component of the causes of mental disorders – e.g. regarding schizophrenia a 50 to 70 % concordance rate was observed in monozygotic twins, whereas a more than two times higher prevalence then expected was observed in adopted children of schizophrenic parents. However, still a certain percentage of schizophrenia is determined by environmental factors. “Soft” diagnostic criteria, rating scales etc. result in different rates of prevalence. New biological methods – imaging, electro-physiology etc. – are completing diagnostic psychiatric procedures. They also have provided new insight into brain correlates of symptoms of mental disorders. Very recently molecular biological data sets were generated by genomics, proteomics etc. The high complexity of these data (high throughput data) cannot be understood and the temporal pattern of on and off genes or the presence of proteins etc. cannot be detected. Additionally, the question is what is the appropriate level of analysis of networks of neurons, their coupling (synapses), the morphology of dendrites (spines), receptors, re uptake mechanisms etc? Therefore, not only computational methods but also systems thinking must be developed in order to retain a comprehensive understanding of mental disorders. Some research strategies are presented.