Stewardship codes comprise a small but important element of the institutional framework supporting a transition towards a more sustainable financial system. By encouraging investors to incorporate environmental, social and governance factors into their investment decisions, these codes can encourage longer-term financial horizons. This chapter explores both the potential of and the challenges for stewardship codes as a tool for improving the sustainability of finance through analysis of twenty-five stewardship codes. It concludes that, by supporting a progressive interpretation of the legal duties of pension fund trustees and company directors, stewardship codes can help harness the financial clout of large investors in steering business towards a more sustainable future. They have the potential to infiltrate the complex modern investment chain, extending the influence of those who think to the long term. Although each code is limited in its enforceability, together stewardship codes have an important role to play within a wider network of mutually reinforcing regulatory instruments pursuing the common goal of sustainable development and securing transparency and accountability.