This paper argues that Israel/Palestine has become a veritable and unparalleled laboratory for assessing and disputing “what is legal” in the context of 21st century war and armed conflict, commencing with the second intifada and accelerating with “Operation Cast Lead.” “Lawfare” refers to the varied uses of law (litigation and other law-centered processes) in the context or aftermath of warfare. Broadly, it involves efforts to interpret, enforce and adjudicate international humanitarian law (IHL—i.e., the contemporary laws of war enshrined in the Geneva Conventions of 1949) against the real-world events occurring or having occurred in an armed conflict. The rules and standards of IHL that have become the subjects of lawfare in Israel/Palestine (and elsewhere) include efforts to identify and penalize war crimes, including violations of civilian immunity (i.e., the prohibition against deliberately targeting civilians and other noncombatants in military operations or otherwise treating them as combatants); distinction (i.e., the imperative to distinguish between civilians and combatants); proportionality (i.e., the injunction to limit the use of force in a manner that is proportional to the military value of the target); necessity (i.e., the imperative to restrict targets or tactics to those necessary to achieve legitimate military goals); and humane treatment (i.e., the prohibition against torture, and cruel, inhumane and degrading treatment of prisoners). While lawfare has been condemned by Israeli officials and supporters of the state’s armed attacks on Palestinians as part of an international campaign of delegitimation (sometimes characterized as a manifestation of anti-Semitism), in fact, the Israeli government has been engaged in an active lawfare campaign of its own in its interpretative efforts to “legalize” extra-judicial assassinations and full-scale military assaults in the still-occupied West Bank and Gaza, and to assert that all Israelis (including soldiers) have legal immunity from attacks while Palestinian civilian immunity is legitimately violable in the pursuit of Israeli security. The paper investigates the “double-edged sword” of lawfare as it has been employed in and on Israel/Palestine to allege and deny Israeli war crimes, and considers how lawfare in this context is contributing to the contemporary instability and fluidity of IHL.