diff --git a/README.md b/README.md
index 750679d..4d1b547 100644
--- a/README.md
+++ b/README.md
@@ -1007,6 +1007,12 @@ Règles modélisées :
    contact pris de dos ne ajoute pas son bonus de Dextérité (« A flat-footed
    creature does not add its Dexterity bonus to its CMD » — la pénalité de
    Dextérité, qui n'est pas un bonus, reste appliquée).
+   (SRD « Trip » / « Bull Rush » / « Overrun ») : « You can only [affect] an
+   opponent who is no more than one size category larger than you » — conformance
+   L8 : trip, bull_rush et overrun contre une cible de **deux catégories de
+   taille ou plus au-dessus** de l'attaquant sont illégaux (tentative refusée,
+   journalisée `rejected (target too large)`, aucun jet, pas d'AoO provoquée) ;
+   les autres manœuvres (disarm, sunder, grapple…) n'ont pas de limite de taille.
    trip → `prone` ; disarm → `disarmed` (−4 attaque) ; bull_rush → pousse la
    cible (direction sélectionnable via `Action.direction`) ; conformance L6
    (SRD « Bull Rush ») : la poussée vaut 5 ft plus « For every 5 by which
diff --git a/src/pf1e_simulator/combat.py b/src/pf1e_simulator/combat.py
index de621e6..edca3ec 100644
--- a/src/pf1e_simulator/combat.py
+++ b/src/pf1e_simulator/combat.py
@@ -262,6 +262,7 @@ _RUN_SPEED_FACTOR = 4  # PF1e: running is a full-round action at 4x speed
 _OVERRUN_PRONE_MARGIN = 5  # PF1e: overrun knocks prone only on a 5+ CMB margin
 _BULL_RUSH_EXTRA_PER_MARGIN = 5  # PF1e: +5 ft push per 5 points above CMD
 _TRIP_RETALIATION_MARGIN = 10  # PF1e: trip failing by 10+ knocks the attacker prone
+_MANEUVER_MAX_SIZE_DIFF = 2  # PF1e: 2+ size categories larger = unmaneuverable
 _SAVE_DESCRIPTOR_CONDITIONS = frozenset({
     "fear", "cold", "electricity", "fey", "divination", "poison", "disease",
     "mind_affecting",
@@ -277,6 +278,24 @@ _SIZE_MODIFIERS: dict[str, int] = {
 # modifier in place of their Strength modifier to determine their CMB.
 _TINY_OR_SMALLER_SIZES: frozenset[str] = frozenset({"tiny", "diminutive", "fine"})
 
+# PF1e size order, smallest first (SRD "Size").
+_SIZE_ORDER: tuple[str, ...] = (
+    "fine", "diminutive", "tiny", "small", "medium", "large", "huge",
+    "gargantuan", "colossal",
+)
+
+# PF1e (SRD Trip / Bull Rush / Overrun): "You can only [affect] an opponent
+# who is no more than one size category larger than you."
+_SIZE_RESTRICTED_MANEUVERS: frozenset[str] = frozenset({"trip", "bull_rush", "overrun"})
+
+
+def _size_rank(size: str) -> int:
+    """Index in the PF1e size order; unknown sizes rank as Medium."""
+    try:
+        return _SIZE_ORDER.index(size.lower())
+    except ValueError:
+        return _SIZE_ORDER.index("medium")
+
 # PF1e natural reach for tall creatures (simplification: no long/quadruped
 # distinction). Unknown sizes fall back to 5 ft (the historical behavior).
 _SIZE_NATURAL_REACH_FT: dict[str, int] = {
@@ -3947,6 +3966,18 @@ class CombatEngine:
             "overrun", "dirty_trick", "steal", "reposition", "drag",
         ):
             return
+        # PF1e (SRD Trip / Bull Rush / Overrun): "You can only [affect] an
+        # opponent who is no more than one size category larger than you."
+        # The attempt is illegal outright: no roll, no provoked AoO.
+        if maneuver in _SIZE_RESTRICTED_MANEUVERS and (
+            _size_rank(target.combatant.size) - _size_rank(state.combatant.size)
+            >= _MANEUVER_MAX_SIZE_DIFF
+        ):
+            self._log(
+                f"round {self._current_round} {state.combatant.id}: {maneuver} vs "
+                f"{target.combatant.id} rejected (target too large)"
+            )
+            return
 
         # PF1e (CRB, Combat Maneuver): attempting the maneuver provokes an
         # attack of opportunity from the target — resolved BEFORE the CMB
diff --git a/tests/test_maneuvers.py b/tests/test_maneuvers.py
index c03a74f..66e8aee 100644
--- a/tests/test_maneuvers.py
+++ b/tests/test_maneuvers.py
@@ -248,6 +248,39 @@ def test_overrun_fail_adjacent_attacker_does_not_move() -> None:
     assert not any("overrun blocked" in line for line in engine._transcript)
 
 
+def test_maneuver_rejects_target_two_sizes_larger() -> None:
+    # SRD Trip/Bull Rush/Overrun: "You can only [affect] an opponent who is
+    # no more than one size category larger than you." Medium vs Huge: the
+    # attempt is illegal — no d20 consumed, no effect, logged rejection.
+    for maneuver in ("trip", "bull_rush", "overrun"):
+        a = make_state(make_combatant("a", attack_bonus=2), "players", (1, 1))
+        huge = make_state(_resized(make_combatant("h"), "Huge", 10, 10), "monsters", (1, 2))
+        engine = make_engine([1, 12], [a, huge])
+        engine._execute_maneuver(a, huge, maneuver)
+        assert len(engine._rng._queue) == 2
+        assert not any(c.condition.name == "prone" for c in huge.active_conditions)
+        assert f"{maneuver} vs h rejected (target too large)" in engine._transcript[-1]
+
+
+def test_maneuver_allows_target_one_size_larger() -> None:
+    # Medium vs Large (one category) stays legal; the roll happens.
+    a = make_state(make_combatant("a", attack_bonus=2), "players", (1, 1))
+    large = make_state(_resized(make_combatant("l"), "Large", 10, 10), "monsters", (1, 2))
+    engine = make_engine([1, 12], [a, large])
+    engine._execute_maneuver(a, large, "trip")
+    assert not engine._rng._queue
+    assert any(c.condition.name == "prone" for c in large.active_conditions)
+
+
+def test_unrestricted_maneuver_ignores_size_limit() -> None:
+    # The size cap is trip/bull_rush/overrun only: disarm works on Huge.
+    a = make_state(make_combatant("a", attack_bonus=2), "players", (1, 1))
+    huge = make_state(_resized(make_combatant("h"), "Huge", 10, 10), "monsters", (1, 2))
+    engine = make_engine([1, 12], [a, huge])
+    engine._execute_maneuver(a, huge, "disarm")
+    assert not engine._rng._queue
+
+
 def test_overrun_knocks_prone_and_moves_through() -> None:
     # d20=15+2=17 vs CMD 12: margin 5 -> prone AND moved through (CRB
     # "Overrun": prone only when the attack exceeds CMD by 5 or more).