After the first five chapters have illustrated the evolution of intergenerational equity from current lex lata to emerging notions of lex ferenda, this chapter turns to the book’s second research question. As the analysis was so far based on the legal regime of the year 2025, it leaves out an intertemporal perspective on intergenerational equity that would preliminary answer which legal regime is actually applicable to the determination of the norm of intergenerational equity de lege lata. Therefore, this chapter elaborates on the doctrine of intertemporal law, which assists in determining the temporally applicable legal regime to an international norm. The first component of intertemporal law, contemporaneity, points to the legal regime contemporaneous to the time of the creation of a certain norm. The second component of intertemporal law contains the application of evolutionary approaches that require taking into account subsequent developments of the legal regime until the time of a dispute on the norm.