In hard law instruments of international humanitarian law, such as treaties and conventions, there is no explicit reference to the concept of reverberating effects related to a military attack. However, the notion of incidental loss of civilian life, injury to civilians, or damage to civilian objects, as stated in the principle of proportionality, is to be interpreted by military forces to include the concept of reverberating impacts. Additionally, under the principle of precautions, the obligation to take constant care to spare civilians and civilian objects must also be applied by military commanders, including an assessment of the reverberating impacts that may result from an attack. This paper aims to examine the key features of the obligation to consider the foreseeable reverberating impacts of a military attack on civilians and civilian objects. It will also explore some of the criteria to consider for determining the reasonable and foreseeable nature of the impacts caused by a lawful or unlawful military attack on civilians.