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/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 4ff05727ebc8ce..6254d046da0319 100644
--- a/Modules/_collectionsmodule.c
+++ b/Modules/_collectionsmodule.c
@@ -1318,7 +1318,7 @@ 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;
 }
 
@@ -1488,7 +1488,7 @@ 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/arraymodule.c b/Modules/arraymodule.c
index a8347123e6496a..bdc752f6161130 100644
--- a/Modules/arraymodule.c
+++ b/Modules/arraymodule.c
@@ -1396,7 +1396,7 @@ 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;
 }
 
@@ -1448,7 +1448,7 @@ 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 0bbf60840a3346..3636bd427a4abf 100644
--- a/Objects/abstract.c
+++ b/Objects/abstract.c
@@ -2214,8 +2214,7 @@ _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 c583193b5a252c..81192570b15dcf 100644
--- a/Objects/bytearrayobject.c
+++ b/Objects/bytearrayobject.c
@@ -94,6 +94,10 @@ typedef PyObject* (*_ba_bytes_op)(const char *buf, Py_ssize_t len,
                                   PyObject *sub, Py_ssize_t start,
                                   Py_ssize_t end);
 
+typedef PyObject* (*_ba_bytes_op2)(const char *buf, Py_ssize_t len,
+                                  PyObject *sub, Py_ssize_t start,
+                                  Py_ssize_t end, const char *classname);
+
 static PyObject *
 _bytearray_with_buffer(PyByteArrayObject *self, _ba_bytes_op op, PyObject *sub,
                        Py_ssize_t start, Py_ssize_t end)
@@ -109,6 +113,22 @@ _bytearray_with_buffer(PyByteArrayObject *self, _ba_bytes_op op, PyObject *sub,
     return res;
 }
 
+static PyObject *
+_bytearray_with_buffer2(PyByteArrayObject *self, _ba_bytes_op2 op, PyObject *sub,
+                       Py_ssize_t start, Py_ssize_t end)
+{
+    PyObject *res;
+
+    _Py_CRITICAL_SECTION_ASSERT_OBJECT_LOCKED(self);
+
+    /* Increase exports to prevent bytearray storage from changing during op. */
+    self->ob_exports++;
+    res = op(PyByteArray_AS_STRING(self), Py_SIZE(self), sub, start, end,
+             "bytearray");
+    self->ob_exports--;
+    return res;
+}
+
 static int
 _canresize(PyByteArrayObject *self)
 {
@@ -1331,7 +1351,7 @@ bytearray_index_impl(PyByteArrayObject *self, PyObject *sub,
                      Py_ssize_t start, Py_ssize_t end)
 /*[clinic end generated code: output=067a1e78efc672a7 input=c37f177cfee19fe4]*/
 {
-    return _bytearray_with_buffer(self, _Py_bytes_index, sub, start, end);
+    return _bytearray_with_buffer2(self, _Py_bytes_index, sub, start, end);
 }
 
 /*[clinic input]
@@ -1367,7 +1387,7 @@ bytearray_rindex_impl(PyByteArrayObject *self, PyObject *sub,
                       Py_ssize_t start, Py_ssize_t end)
 /*[clinic end generated code: output=38e1cf66bafb08b9 input=7d198b3d6b0a62ce]*/
 {
-    return _bytearray_with_buffer(self, _Py_bytes_rindex, sub, start, end);
+    return _bytearray_with_buffer2(self, _Py_bytes_rindex, sub, start, end);
 }
 
 static int
@@ -2336,7 +2356,7 @@ 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 8a9d1b133affb3..db2f98fd617b09 100644
--- a/Objects/bytesobject.c
+++ b/Objects/bytesobject.c
@@ -2052,7 +2052,7 @@ 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]
@@ -2088,7 +2088,7 @@ 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 10e25bbdcdcb6c..cc5d8cc9511188 100644
--- a/Objects/listobject.c
+++ b/Objects/listobject.c
@@ -3350,7 +3350,7 @@ 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;
 }
 
@@ -3420,7 +3420,7 @@ 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 900db864621a84..8b8afa3880082f 100644
--- a/Objects/memoryobject.c
+++ b/Objects/memoryobject.c
@@ -2982,7 +2982,7 @@ 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 55b7f108730728..89f191be80d024 100644
--- a/Objects/rangeobject.c
+++ b/Objects/rangeobject.c
@@ -680,7 +680,7 @@ 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 753c270f525976..255950acba7da6 100644
--- a/Objects/tupleobject.c
+++ b/Objects/tupleobject.c
@@ -681,7 +681,7 @@ 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;
 }