The principle of ‘environmental integrity’ is a fundamental aspect of jus post bellum. Human life, economy, and culture depend on a healthy, functioning environment. However, environmental integrity is a complex concept to describe. Doctrinal thresholds for legally material environmental damage (significant, long-term, widespread) do not capture it. This chapter interrogates the jus post bellum literature and then turns to scholarship on wilderness management in the Anthropocene era, which also engages with the meaning of ‘environmental integrity’, ‘naturalness’, ‘unimpaired’, or, in the words of the Factory at Chorzów case which sets the international law standard for reparations of damage, ‘the situation which would, in all probability, have existed if that act had not been committed’. Recognition that pristine or historical conditions are often impossible to recover or maintain leads to the legal, ethical, and scientific analysis of evolving environmental norms that this chapter offers.