Society today faces unprecedented social and environmental challenges that are both complex in nature and require immediate and severe action. The financial system is a complex system that has an important impact on the sustainable development of society. Currently, however, the role of the finance system in sustainability is ambivalent, as it invests both in the causes of the sustainability challenge as well as its potential solutions. As the finance system is a complex system collaboration is needed to make change possible. Relationships are a key component of collaboration, and this research looks closer at how relationship building can enable effective collaboration aimed at finance systems change. Research draws on Literature, and a case study of the Finance Innovation Lab including 19 qualitative interviews. In order to build collaborative relationships for a sustainable finance system the results point to: 1) the importance of the individual being present in the initiative rather than the organization they represent, and the importance of connecting on personal level; 2) the complexity of relationship building, with different processes and key elements interrelating; and 3) collaborative relationships being only one part of systemic transformation, requiring also a diversity of people and a clear structure and common strategy to be effective in achieving their goals.