None of the major basic questions social sciences are concerned with can satisfyingly be answered from the perspective of one discipline alone. Each of them proposes theories and perspectives that make unique and important contributions. At the same time theoretical perspectives in general inevitably do have their blind spots. This fundamental insight was the reason for us to choose as the motto for the 19th IACCP congress held in Bremen in 2008 “Crossing borders – (Cross - ) Cultural Psychology as an Interdisciplinary, Multi-Method
Endeavor”. In this chapter we first want to illustrate this motto and our reasons for choosing it by reviewing recent research on one exemplary basic question of the social sciences: Can happiness change? We will cover findings across the social science disciplines in order to illustrate the benefits of interdisciplinary, multi - method investigations. This review will also reveal that the recent evidence violates traditional mono- disciplinary views on the respective question. After that, we will briefly introduce the contributions of this volume.