While the term “intergenerational equity” is used in law to describe the legal obligations of the present towards future generations, ideas of “intergenerational justice” have also long been discussed in philosophy to address this relationship between the present and the future. This chapter analyses the complex and intertwined relationship between the legal concept of intergenerational equity and the pre-legal ideas of intergenerational justice. After giving an overview of the most common conceptual objections, particularly the non-identity problem and the non-existence argument, this chapter demonstrates that these obstacles have been overcome by other convincing philosophical considerations. Beyond this, the philosophical realm has shaped the legal discourse of intergenerational equity in many ways. Particularly, John Rawls’ social contract theory, based on just and fair principles of justice, has inspired some aspects of Brown Weiss’ theory on intergenerational equity. Further, communitarian ideas of a transgenerational community of humanity are elaborated on in detail, as they are also reflected in different legal intergenerational notions.