diff --git a/doc/api/next_api_changes/behavior/27514-OG.rst b/doc/api/next_api_changes/behavior/27514-OG.rst
new file mode 100644
index 000000000000..8b2a7ab9ef2e
--- /dev/null
+++ b/doc/api/next_api_changes/behavior/27514-OG.rst
@@ -0,0 +1,5 @@
+Exception when not passing a Bbox to BboxTransform*-classes
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The exception when not passing a Bbox to BboxTransform*-classes that expect one, e.g.,
+`~matplotlib.transforms.BboxTransform` has changed from ``ValueError`` to ``TypeError``.
diff --git a/doc/api/next_api_changes/deprecations/27514-OG.rst b/doc/api/next_api_changes/deprecations/27514-OG.rst
new file mode 100644
index 000000000000..f318ec8aa4bb
--- /dev/null
+++ b/doc/api/next_api_changes/deprecations/27514-OG.rst
@@ -0,0 +1,4 @@
+``TransformNode.is_bbox``
+~~~~~~~~~~~~~~~~~~~~~~~~~
+
+... is deprecated. Instead check the object using ``isinstance(..., BboxBase)``.
diff --git a/lib/matplotlib/transforms.py b/lib/matplotlib/transforms.py
index 5a7fd125a29b..1a68ff12025f 100644
--- a/lib/matplotlib/transforms.py
+++ b/lib/matplotlib/transforms.py
@@ -102,7 +102,7 @@ class TransformNode:
     # Some metadata about the transform, used to determine whether an
     # invalidation is affine-only
     is_affine = False
-    is_bbox = False
+    is_bbox = _api.deprecated("3.9")(_api.classproperty(lambda cls: False))
 
     pass_through = False
     """
@@ -220,7 +220,7 @@ class BboxBase(TransformNode):
     and height, but these are not stored explicitly.
     """
 
-    is_bbox = True
+    is_bbox = _api.deprecated("3.9")(_api.classproperty(lambda cls: True))
     is_affine = True
 
     if DEBUG:
@@ -1101,8 +1101,7 @@ def __init__(self, bbox, transform, **kwargs):
         bbox : `Bbox`
         transform : `Transform`
         """
-        if not bbox.is_bbox:
-            raise ValueError("'bbox' is not a bbox")
+        _api.check_isinstance(BboxBase, bbox=bbox)
         _api.check_isinstance(Transform, transform=transform)
         if transform.input_dims != 2 or transform.output_dims != 2:
             raise ValueError(
@@ -1190,9 +1189,7 @@ def __init__(self, bbox, x0=None, y0=None, x1=None, y1=None, **kwargs):
             The locked value for y1, or None to leave unlocked.
 
         """
-        if not bbox.is_bbox:
-            raise ValueError("'bbox' is not a bbox")
-
+        _api.check_isinstance(BboxBase, bbox=bbox)
         super().__init__(**kwargs)
         self._bbox = bbox
         self.set_children(bbox)
@@ -2547,8 +2544,7 @@ def __init__(self, boxin, boxout, **kwargs):
         Create a new `BboxTransform` that linearly transforms
         points from *boxin* to *boxout*.
         """
-        if not boxin.is_bbox or not boxout.is_bbox:
-            raise ValueError("'boxin' and 'boxout' must be bbox")
+        _api.check_isinstance(BboxBase, boxin=boxin, boxout=boxout)
 
         super().__init__(**kwargs)
         self._boxin = boxin
@@ -2591,8 +2587,7 @@ def __init__(self, boxout, **kwargs):
         Create a new `BboxTransformTo` that linearly transforms
         points from the unit bounding box to *boxout*.
         """
-        if not boxout.is_bbox:
-            raise ValueError("'boxout' must be bbox")
+        _api.check_isinstance(BboxBase, boxout=boxout)
 
         super().__init__(**kwargs)
         self._boxout = boxout
@@ -2645,8 +2640,7 @@ class BboxTransformFrom(Affine2DBase):
     is_separable = True
 
     def __init__(self, boxin, **kwargs):
-        if not boxin.is_bbox:
-            raise ValueError("'boxin' must be bbox")
+        _api.check_isinstance(BboxBase, boxin=boxin)
 
         super().__init__(**kwargs)
         self._boxin = boxin