Closing the financial gap for promoting systemic socio-economic transformations to achieve sustainability requires both a substantial increase in investment levels and a qualitative change in investment strategies. In this Perspective, we elaborate on this claim and discuss why existing investment approaches that aim to make positive contributions to sustainability are unlikely to foster the systemic transformations needed for sustainability. Qualitative change means changing the current rules that guide investment practices and we outline a new set of rules that should guide transformative investment. These rules are based on the well-established socio-technical sustainability transition theory and the recent development of a theory of deep transitions. We explain why these transformative investment rules offer a promising alternative base for assessing investment opportunities and monitoring progress toward the multi-system changes required to achieve a socially just deep transition to sustainability.