The paper deals with financialisation of capitalist economies since the 1990s drawing on a conventional concept of economic rationalities. It is argued that financial rationality is not the mere outcome of relations of power rooted elsewhere but a power resource on its own. It is analysed as one type of bounded rationality among others, the recent predominance of which traces back mainly to a paradigmatic shift in economics. However predominance does not mean unambiguousness. It is demonstrated that financial rationality on the level of companies or companies’ strategies always has to be interpreted and specified in the perspective of other rationalities. And effective financialised strategies are always the outcome of bargaining between social actors bringing into play various interests, power resources, and rationalities. The financial and economic crisis since 2007 is perceived as symptomatic for a new kind of systemic instabilities caused by the predominance of financial rationality.