This paper argues that existing human-animal relations contribute to the pressing socio-ecological crises of our time, and therefore, they should be discussed in the context of Sustainable Development. This holds true even from a purely anthropocentric perspective, as these crises are threats to humans. However, sentient nonhuman animals possess interests as well and should be included in the moral community. Therefore, ignoring their interests in Sustainable Development is falling short. Furthermore, the paper argues that the anthropocentric perspective of Sustainable Development (...) is flawed because the normative foundations of Sustainable Development (intra- and intergenerational justice) can be convincingly applied to nonhuman animals. According to approaches of interspecies justice, the normative foundations of Sustainable Development not merely can but should be applied to nonhuman animals. The paper argues for including nonhuman animals into the scope of justice and, therefore, in a theory of Sustainable Development. What such inclusion means at the practical level is examined in the last section of the paper, which investigates a field of application important for transforming societies into more sustainable ones, namely energy systems. This last section discusses how more sustainable, more animal-friendly energy systems would look like. (shrink)