The present thesis provides a theoretical overview, including a neurobiological perspective, of well-being (WB), eudaimonic well-being (EWB), optimism, pessimism and cultural differences between Western and Eastern societies. In addition, an empirical study investigated these concepts in Japanese and Swedish participants. Definitional problems and scarce neurobiological findings are two current problems to date within research on WB, EWB and cultural differences especially when looking at comparisons between Europe and East Asia. Interpretations and conclusions are therefore hard and tentative to make as more research is yet needed. This thesis empirical part therefore investigated the association between these concepts. In the best of the authors knowledge have this type of explorative study never been done before. 142 Swedish participants and 68 Japanese participants between the ages of 20 to 40 answered the self-reporting questionnaires; revised life orientation test (LOT-R), psychological well-being scale (SPWB) and the minimalist well-being scale (MWBS). The findings demonstrate that Swedish people report higher levels of optimism compared with Japanese people whom in turn report higher levels of pessimism when measured with LOT-R. Findings further demonstrate that Swedish people report higher levels of EWB when measured with SPWB. In comparison do Japanese people report higher levels of EWB when measured with MWBS. A difference was found in response pattern between MWBS and SPWB. And last did the findings suggest correlations in total scores of MWBS, SPWB and LOT-R but not within all sub-dimensions. Discussion of the results, limitations of the thesis and suggestions for future research concludes the thesis.