Rule 17. Choice of Means and Methods of Warfare
Rule 17. Each party to the conflict must take all feasible precautions in the choice of means and methods of warfare with a view to avoiding, and in any event to minimizing, incidental loss of civilian life, injury to civilians and damage to civilian objects.
Summary
State practice establishes this rule as a norm of customary international law applicable in international and non-international armed conflicts. This rule must be applied independently of the simultaneous application of the principle of proportionality (see Rule 14).
International armed conflicts
The duty to take all feasible precautions in the choice of means and methods of warfare is set forth in Article 57(2)(a)(ii) of Additional Protocol I, to which no relevant reservations have been made.[1] 
This obligation is included in numerous military manuals.[2]  It is also supported by official statements and reported practice.[3]  This practice includes that of States not, or not at the time, party to Additional Protocol I.[4]  When the ICRC appealed to the parties to the conflict in the Middle East in October 1973, i.e., before the adoption of Additional Protocol I, to take all feasible precautions in the choice of means and methods of warfare, the States concerned (Egypt, Iraq, Israel and Syrian Arab Republic) replied favourably.[5] 
Non-international armed conflicts
While Additional Protocol II does not include an explicit reference to the obligation to take all feasible precautions in the choice of means and methods of warfare, more recent treaty law applicable in non-international armed conflicts does so, namely the Second Protocol to the Hague Convention for the Protection of Cultural Property.[6]  In addition, this rule is contained in other instruments pertaining also to non-international armed conflicts.[7] 
This rule is set forth in military manuals which are applicable in or have been applied in non-international armed conflicts.[8] 
The jurisprudence of the International Criminal Tribunal for the Former Yugoslavia and of the European Court of Human Rights provides further evidence of the customary nature of this rule in both international and non-international armed conflicts.[9]  In its judgment in the Kupreškić case, the International Criminal Tribunal for the Former Yugoslavia considered that this rule was customary because it specified and fleshed out general pre-existing norms.[10]  It can be argued indeed that the principle of distinction, which is customary in international and non-international armed conflicts, inherently requires respect for this rule. The Tribunal also relied on the fact that this rule had not been contested by any State.[11]  This study found no official contrary practice either.
Examples
Examples of the application of this rule include considerations about the timing of attacks, avoiding combat in populated areas, the selection of means of warfare proportionate to the target, the use of precision weapons and target selection. In addition, Rule 21 sets out a specific requirement with respect to target selection.

[1] Additional Protocol I, Article 57(2)(a)(ii) (adopted by 90 votes in favour, none against and 4 abstentions) (cited in Vol. II, Ch. 5, § 265).
[2] See, e.g., the military manuals of Argentina (ibid., § 271), Australia (ibid., § 272), Benin (ibid., § 273), Cameroon (ibid., § 274), Canada (ibid., § 275), Croatia (ibid., §§ 276–277), Ecuador (ibid., § 278), France (ibid., § 279), Germany (ibid., § 280), Hungary (ibid., § 281), Israel (ibid., § 282), Italy (ibid., § 283), Kenya (ibid., § 284), Madagascar (ibid., § 285), Netherlands (ibid., § 286), New Zealand (ibid., § 287), Philippines (ibid., § 288), Spain (ibid., § 289), Sweden (ibid., § 290), Togo (ibid., § 291), United Kingdom (ibid., § 292), United States (ibid., §§ 293–294) and Yugoslavia (ibid., § 295).
[3] See, e.g., the statements of Indonesia (ibid., § 299), Iraq (ibid., § 301), Japan (ibid., § 303), Netherlands (ibid., § 305), United Kingdom (ibid., §§ 307–308) and United States (ibid., §§ 309–311) and the reported practice of the Islamic Republic of Iran (ibid., § 300), Israel (ibid., § 302), Malaysia (ibid., § 304), Syrian Arab Republic (ibid., § 306) and Zimbabwe (ibid., § 312).
[4] See, e.g., the practice of Indonesia (ibid., § 299), Iraq (ibid., § 301), Israel (ibid., § 282), Japan (ibid., § 303), Kenya (ibid., § 284), United Kingdom (ibid., §§ 292 and 307–308) and United States (ibid., §§ 293–294 and 309–311) and the reported practice of the Islamic Republic of Iran (ibid., § 300), Israel (ibid., § 302) and Malaysia (ibid., § 304).
[5] See ICRC, The International Committee’s Action in the Middle East (ibid., § 263).
[6] Second Protocol to the Hague Convention for the Protection of Cultural Property, Article 7 (ibid., § 208).
[7] See, e.g., Memorandum of Understanding on the Application of IHL between Croatia and the Socialist Federal Republic of Yugoslavia, § 6 (ibid., § 268); Agreement on the Application of IHL between the Parties to the Conflict in Bosnia and Herzegovina, § 2.5 (ibid., § 269); San Remo Manual, § 46(c) (ibid., § 270).
[8] See, e.g., the military manuals of Benin (ibid., § 273), Croatia (ibid., §§ 276–277), Ecuador (ibid., § 278), Germany (ibid., § 280), Italy (ibid., § 283), Kenya (ibid., § 284), Madagascar (ibid., § 285), Philippines (ibid., § 288), Togo (ibid., § 291) and Yugoslavia (ibid., § 295).
[9] ICTY, Kupreškić case, Judgment (ibid., § 260); European Court of Human Rights, Ergi v. Turkey (ibid., § 319).
[10] ICTY, Kupreškić case, Judgment (ibid., § 260).
[11] ICTY, Kupreškić case, Judgment (ibid., § 260).