diff --git a/CHANGELOG.md b/CHANGELOG.md
index ad876d36bf0..127343dec2a 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -22,6 +22,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   ([#2044](https://github.com/open-telemetry/opentelemetry-python/pull/2044))
 - `opentelemetry-sdk` Add support for `OTEL_ATTRIBUTE_VALUE_LENGTH_LIMIT` env var
   ([#2056](https://github.com/open-telemetry/opentelemetry-python/pull/2056))
+- `opentelemetry-api` Attribute keys must be non-empty strings.
+  ([#2057](https://github.com/open-telemetry/opentelemetry-python/pull/2057))
 
 ## [0.23.1](https://github.com/open-telemetry/opentelemetry-python/pull/1987) - 2021-07-26
 
diff --git a/opentelemetry-api/src/opentelemetry/attributes/__init__.py b/opentelemetry-api/src/opentelemetry/attributes/__init__.py
index 877f98e8be4..a266839326a 100644
--- a/opentelemetry-api/src/opentelemetry/attributes/__init__.py
+++ b/opentelemetry-api/src/opentelemetry/attributes/__init__.py
@@ -47,8 +47,8 @@ def _clean_attribute(
         - It needs to be encoded/decoded e.g, bytes to strings.
     """
 
-    if key is None or key == "":
-        _logger.warning("invalid key `%s` (empty or null)", key)
+    if not (key and isinstance(key, str)):
+        _logger.warning("invalid key `%s`. must be non-empty string.", key)
         return None
 
     if isinstance(value, _VALID_ATTR_VALUE_TYPES):
@@ -118,7 +118,7 @@ def _clean_attribute_value(
     if isinstance(value, bytes):
         try:
             value = value.decode()
-        except ValueError:
+        except UnicodeDecodeError:
             _logger.warning("Byte attribute could not be decoded.")
             return None
 
diff --git a/opentelemetry-api/tests/attributes/test_attributes.py b/opentelemetry-api/tests/attributes/test_attributes.py
index 045c1f7125c..fa0606b347c 100644
--- a/opentelemetry-api/tests/attributes/test_attributes.py
+++ b/opentelemetry-api/tests/attributes/test_attributes.py
@@ -31,6 +31,16 @@ def assertValid(self, value, key="k"):
     def assertInvalid(self, value, key="k"):
         self.assertIsNone(_clean_attribute(key, value, None))
 
+    def test_attribute_key_validation(self):
+        # only non-empty strings are valid keys
+        self.assertInvalid(1, "")
+        self.assertInvalid(1, 1)
+        self.assertInvalid(1, {})
+        self.assertInvalid(1, [])
+        self.assertInvalid(1, b"1")
+        self.assertValid(1, "k")
+        self.assertValid(1, "1")
+
     def test_clean_attribute(self):
         self.assertInvalid([1, 2, 3.4, "ss", 4])
         self.assertInvalid([dict(), 1, 2, 3.4, 4])
@@ -142,10 +152,10 @@ def test_bounded_dict(self):
     def test_no_limit_code(self):
         bdict = BoundedAttributes(maxlen=None, immutable=False)
         for num in range(100):
-            bdict[num] = num
+            bdict[str(num)] = num
 
         for num in range(100):
-            self.assertEqual(bdict[num], num)
+            self.assertEqual(bdict[str(num)], num)
 
     def test_immutable(self):
         bdict = BoundedAttributes()
diff --git a/opentelemetry-sdk/src/opentelemetry/sdk/trace/__init__.py b/opentelemetry-sdk/src/opentelemetry/sdk/trace/__init__.py
index 7acffecd85f..249057aef78 100644
--- a/opentelemetry-sdk/src/opentelemetry/sdk/trace/__init__.py
+++ b/opentelemetry-sdk/src/opentelemetry/sdk/trace/__init__.py
@@ -536,6 +536,12 @@ class SpanLimits:
       environment variable.
     - If the environment variable is not set, the default value for the limit is used.
 
+    Limit precedence:
+    
+    - If a model specific limit is set, it will be used.
+    - Else if the model specific limit has a default value, the default value will be used.
+    - Else if model specific limit has a corresponding global limit, the global limit will be used. 
+
     Args:
         max_attributes: Maximum number of attributes that can be added to a Span.
             Environment variable: OTEL_SPAN_ATTRIBUTE_COUNT_LIMIT
@@ -593,10 +599,6 @@ def __init__(
             OTEL_LINK_ATTRIBUTE_COUNT_LIMIT,
             _DEFAULT_OTEL_LINK_ATTRIBUTE_COUNT_LIMIT,
         )
-        self.max_attribute_length = self._from_env_if_absent(
-            max_attribute_length,
-            OTEL_SPAN_ATTRIBUTE_VALUE_LENGTH_LIMIT,
-        )
 
         self.max_attribute_length = self._from_env_if_absent(
             max_attribute_length,