diff --git a/Include/internal/pycore_bytes_methods.h b/Include/internal/pycore_bytes_methods.h
index 3e1474c1c010f9..02bd8c53c1e126 100644
--- a/Include/internal/pycore_bytes_methods.h
+++ b/Include/internal/pycore_bytes_methods.h
@@ -29,11 +29,13 @@ extern void _Py_bytes_swapcase(char *result, const char *s, Py_ssize_t len);
 extern PyObject *_Py_bytes_find(const char *str, Py_ssize_t len, PyObject *sub,
                                 Py_ssize_t start, Py_ssize_t end);
 extern PyObject *_Py_bytes_index(const char *str, Py_ssize_t len, PyObject *sub,
-                                 Py_ssize_t start, Py_ssize_t end);
+                                 Py_ssize_t start, Py_ssize_t end,
+                                 const char *classname);
 extern PyObject *_Py_bytes_rfind(const char *str, Py_ssize_t len, PyObject *sub,
                                  Py_ssize_t start, Py_ssize_t end);
 extern PyObject *_Py_bytes_rindex(const char *str, Py_ssize_t len, PyObject *sub,
-                                 Py_ssize_t start, Py_ssize_t end);
+                                 Py_ssize_t start, Py_ssize_t end,
+                                 const char *classname);
 extern PyObject *_Py_bytes_count(const char *str, Py_ssize_t len, PyObject *sub,
                                  Py_ssize_t start, Py_ssize_t end);
 extern int _Py_bytes_contains(const char *str, Py_ssize_t len, PyObject *arg);
diff --git a/Lib/operator.py b/Lib/operator.py
index 1b765522f85949..9268ef35e7ea9a 100644
--- a/Lib/operator.py
+++ b/Lib/operator.py
@@ -184,7 +184,7 @@ def indexOf(a, b):
         if j is b or j == b:
             return i
     else:
-        raise ValueError('sequence.index(x): x not in sequence')
+        raise ValueError('value not in sequence')
 
 def setitem(a, b, c):
     "Same as a[b] = c."
diff --git a/Lib/test/test_xml_etree.py b/Lib/test/test_xml_etree.py
index f65baa0cfae2ad..02b5b2b6c18657 100644
--- a/Lib/test/test_xml_etree.py
+++ b/Lib/test/test_xml_etree.py
@@ -371,7 +371,7 @@ def test_simpleops(self):
         element.remove(subelement)
         self.serialize_check(element, '<tag key="value" />') # 5
         with self.assertRaisesRegex(ValueError,
-                                    r'Element\.remove\(.+\): element not found'):
+                                    r"<Element 'subtag'.*> not in <Element 'tag'.*>"):
             element.remove(subelement)
         self.serialize_check(element, '<tag key="value" />') # 6
         element[0:0] = [subelement, subelement, subelement]
diff --git a/Lib/xml/etree/ElementTree.py b/Lib/xml/etree/ElementTree.py
index dafe5b1b8a0c3f..f4306a3cafb11a 100644
--- a/Lib/xml/etree/ElementTree.py
+++ b/Lib/xml/etree/ElementTree.py
@@ -271,7 +271,7 @@ def remove(self, subelement):
             self._children.remove(subelement)
         except ValueError:
             # to align the error message with the C implementation
-            raise ValueError("Element.remove(x): element not found") from None
+            raise ValueError(f"{subelement!r} not in {self!r}") from None
 
     def find(self, path, namespaces=None):
         """Find first matching element by tag name or path.
diff --git a/Misc/NEWS.d/next/Core_and_Builtins/2025-10-07-18-20-33.gh-issue-137508.Llt4Ei.rst b/Misc/NEWS.d/next/Core_and_Builtins/2025-10-07-18-20-33.gh-issue-137508.Llt4Ei.rst
new file mode 100644
index 00000000000000..5458b17ffd941d
--- /dev/null
+++ b/Misc/NEWS.d/next/Core_and_Builtins/2025-10-07-18-20-33.gh-issue-137508.Llt4Ei.rst
@@ -0,0 +1,5 @@
+Unify error messages for the :meth:`!index` and :meth:`!remove` methods of
+classes :class:`list`, :class:`tuple`, :class:`range`, :class:`memoryview`,
+:class:`str`, :class:`bytes`, :class:`bytearray`, :class:`array.array`, and
+:class:`collections.deque`, and the :func:`operator.indexOf` function.
+Improve error message for :meth:`xml.etree.ElementTree.Element.remove`.
diff --git a/Modules/_collectionsmodule.c b/Modules/_collectionsmodule.c
index 3ba48d5d9d3c64..dba7e8a3765a45 100644
--- a/Modules/_collectionsmodule.c
+++ b/Modules/_collectionsmodule.c
@@ -1302,7 +1302,7 @@ deque_index_impl(dequeobject *deque, PyObject *v, Py_ssize_t start,
             index = 0;
         }
     }
-    PyErr_SetString(PyExc_ValueError, "deque.index(x): x not in deque");
+    PyErr_SetString(PyExc_ValueError, "value not in deque");
     return NULL;
 }
 
@@ -1472,7 +1472,7 @@ deque_remove_impl(dequeobject *deque, PyObject *value)
         }
     }
     if (i == n) {
-        PyErr_SetString(PyExc_ValueError, "deque.remove(x): x not in deque");
+        PyErr_SetString(PyExc_ValueError, "value not in deque");
         return NULL;
     }
     rv = deque_del_item(deque, i);
diff --git a/Modules/_elementtree.c b/Modules/_elementtree.c
index 9263f14b57f972..6923f2bcc05763 100644
--- a/Modules/_elementtree.c
+++ b/Modules/_elementtree.c
@@ -1679,8 +1679,7 @@ _elementtree_Element_remove_impl(ElementObject *self, PyObject *subelement)
     }
 
     if (rc == 0) {
-        PyErr_SetString(PyExc_ValueError,
-                        "Element.remove(x): element not found");
+        PyErr_Format(PyExc_ValueError, "%R not in %R", subelement, self);
         return NULL;
     }
 
diff --git a/Modules/arraymodule.c b/Modules/arraymodule.c
index d97cf7af767ca3..f0789b71eabae3 100644
--- a/Modules/arraymodule.c
+++ b/Modules/arraymodule.c
@@ -1233,7 +1233,7 @@ array_array_index_impl(arrayobject *self, PyObject *v, Py_ssize_t start,
         else if (cmp < 0)
             return NULL;
     }
-    PyErr_SetString(PyExc_ValueError, "array.index(x): x not in array");
+    PyErr_SetString(PyExc_ValueError, "value not in array");
     return NULL;
 }
 
@@ -1285,7 +1285,7 @@ array_array_remove_impl(arrayobject *self, PyObject *v)
         else if (cmp < 0)
             return NULL;
     }
-    PyErr_SetString(PyExc_ValueError, "array.remove(x): x not in array");
+    PyErr_SetString(PyExc_ValueError, "value not in array");
     return NULL;
 }
 
diff --git a/Objects/abstract.c b/Objects/abstract.c
index 8adad8407d04d4..297193dcc44cb5 100644
--- a/Objects/abstract.c
+++ b/Objects/abstract.c
@@ -2206,8 +2206,7 @@ _PySequence_IterSearch(PyObject *seq, PyObject *obj, int operation)
     if (operation != PY_ITERSEARCH_INDEX)
         goto Done;
 
-    PyErr_SetString(PyExc_ValueError,
-                    "sequence.index(x): x not in sequence");
+    PyErr_SetString(PyExc_ValueError, "value not in sequence");
     /* fall into failure code */
 Fail:
     n = -1;
diff --git a/Objects/bytearrayobject.c b/Objects/bytearrayobject.c
index c519485c1cc74c..6f4b655da2f77a 100644
--- a/Objects/bytearrayobject.c
+++ b/Objects/bytearrayobject.c
@@ -1293,7 +1293,7 @@ bytearray_index_impl(PyByteArrayObject *self, PyObject *sub,
 /*[clinic end generated code: output=067a1e78efc672a7 input=c37f177cfee19fe4]*/
 {
     return _Py_bytes_index(PyByteArray_AS_STRING(self), PyByteArray_GET_SIZE(self),
-                           sub, start, end);
+                           sub, start, end, "bytearray");
 }
 
 /*[clinic input]
@@ -1331,7 +1331,7 @@ bytearray_rindex_impl(PyByteArrayObject *self, PyObject *sub,
 /*[clinic end generated code: output=38e1cf66bafb08b9 input=7d198b3d6b0a62ce]*/
 {
     return _Py_bytes_rindex(PyByteArray_AS_STRING(self), PyByteArray_GET_SIZE(self),
-                            sub, start, end);
+                            sub, start, end, "bytearray");
 }
 
 static int
@@ -2207,7 +2207,7 @@ bytearray_remove_impl(PyByteArrayObject *self, int value)
 
     where = stringlib_find_char(buf, n, value);
     if (where < 0) {
-        PyErr_SetString(PyExc_ValueError, "value not found in bytearray");
+        PyErr_SetString(PyExc_ValueError, "value not in bytearray");
         return NULL;
     }
     if (!_canresize(self))
diff --git a/Objects/bytes_methods.c b/Objects/bytes_methods.c
index 56a461d0dd08a7..5c78c2cecab732 100644
--- a/Objects/bytes_methods.c
+++ b/Objects/bytes_methods.c
@@ -521,14 +521,18 @@ _Py_bytes_find(const char *str, Py_ssize_t len, PyObject *sub,
 
 PyObject *
 _Py_bytes_index(const char *str, Py_ssize_t len, PyObject *sub,
-                Py_ssize_t start, Py_ssize_t end)
+                Py_ssize_t start, Py_ssize_t end, const char *classname)
 {
     Py_ssize_t result = find_internal(str, len, "index", sub, start, end, +1);
     if (result == -2)
         return NULL;
     if (result == -1) {
-        PyErr_SetString(PyExc_ValueError,
-                        "subsection not found");
+        if (PyIndex_Check(sub)) {
+            PyErr_Format(PyExc_ValueError, "value not in %s", classname);
+        }
+        else {
+            PyErr_SetString(PyExc_ValueError, "subsection not found");
+        }
         return NULL;
     }
     return PyLong_FromSsize_t(result);
@@ -546,14 +550,15 @@ _Py_bytes_rfind(const char *str, Py_ssize_t len, PyObject *sub,
 
 PyObject *
 _Py_bytes_rindex(const char *str, Py_ssize_t len, PyObject *sub,
-                 Py_ssize_t start, Py_ssize_t end)
+                 Py_ssize_t start, Py_ssize_t end, const char *classname)
 {
     Py_ssize_t result = find_internal(str, len, "rindex", sub, start, end, -1);
     if (result == -2)
         return NULL;
     if (result == -1) {
-        PyErr_SetString(PyExc_ValueError,
-                        "subsection not found");
+        PyErr_Format(PyExc_ValueError, "%s not in %s",
+                     PyIndex_Check(sub) ? "value" : "subsection",
+                     classname);
         return NULL;
     }
     return PyLong_FromSsize_t(result);
diff --git a/Objects/bytesobject.c b/Objects/bytesobject.c
index de8ab26db1e966..816210c3665c9e 100644
--- a/Objects/bytesobject.c
+++ b/Objects/bytesobject.c
@@ -1965,7 +1965,7 @@ bytes_index_impl(PyBytesObject *self, PyObject *sub, Py_ssize_t start,
 /*[clinic end generated code: output=0da25cc74683ba42 input=1cb45ce71456a269]*/
 {
     return _Py_bytes_index(PyBytes_AS_STRING(self), PyBytes_GET_SIZE(self),
-                           sub, start, end);
+                           sub, start, end, "bytes");
 }
 
 /*[clinic input]
@@ -2001,7 +2001,7 @@ bytes_rindex_impl(PyBytesObject *self, PyObject *sub, Py_ssize_t start,
 /*[clinic end generated code: output=42bf674e0a0aabf6 input=bb5f473c64610c43]*/
 {
     return _Py_bytes_rindex(PyBytes_AS_STRING(self), PyBytes_GET_SIZE(self),
-                            sub, start, end);
+                            sub, start, end, "bytes");
 }
 
 
diff --git a/Objects/listobject.c b/Objects/listobject.c
index 5905a6d335b311..bbf8341b91dd80 100644
--- a/Objects/listobject.c
+++ b/Objects/listobject.c
@@ -3306,7 +3306,7 @@ list_index_impl(PyListObject *self, PyObject *value, Py_ssize_t start,
         else if (cmp < 0)
             return NULL;
     }
-    PyErr_SetString(PyExc_ValueError, "list.index(x): x not in list");
+    PyErr_SetString(PyExc_ValueError, "value not in list");
     return NULL;
 }
 
@@ -3376,7 +3376,7 @@ list_remove_impl(PyListObject *self, PyObject *value)
         else if (cmp < 0)
             return NULL;
     }
-    PyErr_SetString(PyExc_ValueError, "list.remove(x): x not in list");
+    PyErr_SetString(PyExc_ValueError, "value not in list");
     return NULL;
 }
 
diff --git a/Objects/memoryobject.c b/Objects/memoryobject.c
index f1232f389210ea..26b3540ac3410a 100644
--- a/Objects/memoryobject.c
+++ b/Objects/memoryobject.c
@@ -2894,7 +2894,7 @@ memoryview_index_impl(PyMemoryViewObject *self, PyObject *value,
             }
         }
 
-        PyErr_SetString(PyExc_ValueError, "memoryview.index(x): x not found");
+        PyErr_SetString(PyExc_ValueError, "value not in memoryview");
         return NULL;
     }
 
diff --git a/Objects/rangeobject.c b/Objects/rangeobject.c
index f8cdfe68a6435e..0a6d21d52ce8cc 100644
--- a/Objects/rangeobject.c
+++ b/Objects/rangeobject.c
@@ -665,7 +665,7 @@ range_index(PyObject *self, PyObject *ob)
     }
 
     /* object is not in the range */
-    PyErr_SetString(PyExc_ValueError, "range.index(x): x not in range");
+    PyErr_SetString(PyExc_ValueError, "value not in range");
     return NULL;
 }
 
diff --git a/Objects/tupleobject.c b/Objects/tupleobject.c
index 1fa4bae638a1fe..a80a392a079b31 100644
--- a/Objects/tupleobject.c
+++ b/Objects/tupleobject.c
@@ -585,7 +585,7 @@ tuple_index_impl(PyTupleObject *self, PyObject *value, Py_ssize_t start,
         else if (cmp < 0)
             return NULL;
     }
-    PyErr_SetString(PyExc_ValueError, "tuple.index(x): x not in tuple");
+    PyErr_SetString(PyExc_ValueError, "value not in tuple");
     return NULL;
 }