For the legal specialist approaching any IHL issue, the beginning of wisdom lies in the answers to the questions: What law is applicable in this particular situation? Is it treaty law, applicable because the State or States concerned signed and ratified such-and-such a treaty when it was made, or acceded to it later? Or is it, in whole or in part, customary law, which is applicable to all States, no matter whether or not they would have wished to accede to it if the choice had been open to them?1 Application may therefore be broad or narrow, dubious or certain, according to the mixture of elements in each particular case: the nature of the situation which makes application of IHL a possibility, and the extent to which the State or States in the case are involved, either by their treaty undertakings or by customary obligation. Always a State or States will appear in the front line, because public international law has until quite recently been very reluctant to recognize any but States as its (to use its own language) subjects, persons, or actors.
The question of the application and applicability of IHL has a different aspect for humanitarian persons and organizations striving actually to make it useful in given situations. The fact is that it may practically be applied where it is not, in strictly legal terms, applicable. Examples in this book have shown how States sometimes dismiss their legal obligations as mere scraps of paper or pick and choose among them which they will observe and which they won't. On the other hand we see that IHL can make its way into situations where its legal applicability is by no means clear. To the bulk of the persons and organizations dedicated to its service, this mismatch between the letter and the spirit of the law is of no importance except to the extent that unfriendly States, resting on its letter and on their lawyers' ingenuity in making the most of it, may use their legal rights to obstructive effect.
To speak of the application of IHL as a practical matter is to speak of what many people would call its implementation. For the whole of the____________________