Environmental harm during armed conflict is a cross-cutting issue that comes within the remit of both international humanitarian law (IHL) and international environmental law (IEL). Yet, until recently, the interrelationship between these two “neighbouring” frameworks has been underexplored, leading to a need for in-depth analysis of how norms from the two frameworks interact and consideration as to whether they can be harmonised. By identifying key gaps and uncertainties within the IHL targeting framework and corresponding precautionary duties as applied to the environment, this chapter examines the extent to which the IEL prevention principle can inform these. It does so through the lens of treaty interpretation, in particular the method of systemic integration reflected in Article 31(3)(c) of the Vienna Convention on the Law of Treaties. By examining the IEL prevention principle and IHL precautionary duties side by side and setting out where and how they intersect, this chapter demonstrates the need for and potential of such analyses to standardise processes and decision-making that entail collateral environmental harm during the conduct of hostilities, with a view to providing greater environmental protection.