This chapter explores the legal framework for ESG investor engagement and, in so doing, favours a market-led approach over prescriptive regulatory intervention. I argue that investor initiatives and engagement are and should be the primary tool to promote sustainability orientation in the market. Legislative measures are deemed most effective when empowering investor engagement, enhancing transparency in sustainability criteria, and addressing greenwashing concerns. The need to build coalitions and to convince fellow investors of an initiative can then act as an in-built “filter”, which would help mitigate the pursuit of merely idiosyncratic motives and would give support to only those campaigns that are supported by a majority of investors. In particular, institutionalised investor platforms have emerged over recent years to coordinate investor campaigns and to share costs. Accordingly, I conclude with the policy implication that lawmakers should take a supportive and facilitative approach that supports investor engagement and private ordering. By doing so, static and interventionist legal policies would become less justified.