diff --git a/doc/source/io.rst b/doc/source/io.rst
index 0c31bfe014a12..bd81b478b5326 100644
--- a/doc/source/io.rst
+++ b/doc/source/io.rst
@@ -226,7 +226,7 @@ NA and Missing Data Handling
 na_values : scalar, str, list-like, or dict, default ``None``
   Additional strings to recognize as NA/NaN. If dict passed, specific per-column
   NA values. By default the following values are interpreted as NaN:
-  ``'-1.#IND', '1.#QNAN', '1.#IND', '-1.#QNAN', '#N/A N/A', '#N/A', 'N/A', 'NA',
+  ``'-1.#IND', '1.#QNAN', '1.#IND', '-1.#QNAN', '#N/A N/A', '#N/A', 'N/A', 'n/a', 'NA',
   '#NA', 'NULL', 'null', 'NaN', '-NaN', 'nan', '-nan', ''``.
 keep_default_na : boolean, default ``True``
   If na_values are specified and keep_default_na is ``False`` the default NaN
diff --git a/doc/source/whatsnew/v0.21.0.txt b/doc/source/whatsnew/v0.21.0.txt
index 6dad03f086a6c..3dd8bb2ac2de5 100644
--- a/doc/source/whatsnew/v0.21.0.txt
+++ b/doc/source/whatsnew/v0.21.0.txt
@@ -38,7 +38,7 @@ Other Enhancements
 - :func:`read_feather` has gained the ``nthreads`` parameter for multi-threaded operations (:issue:`16359`)
 - :func:`DataFrame.clip()` and :func: `Series.cip()` have gained an inplace argument. (:issue: `15388`)
 - :func:`crosstab` has gained a ``margins_name`` parameter to define the name of the row / column that will contain the totals when margins=True. (:issue:`15972`)
-- :func:`read_csv` has gained 'null' as an additional default missing value.(:issue:`16471`)
+
 .. _whatsnew_0210.api_breaking:
 
 Backwards incompatible API changes
@@ -49,6 +49,8 @@ Backwards incompatible API changes
 
 - Accessing a non-existent attribute on a closed :class:`HDFStore` will now
   raise an ``AttributeError`` rather than a ``ClosedFileError`` (:issue:`16301`)
+- :func:`read_csv` now treats ``'null'`` strings as missing values by default (:issue:`16471`)
+- :func:`read_csv` now treats ``'n/a'`` strings as missing values by default (:issue:`16078`)
 
 .. _whatsnew_0210.api:
 
diff --git a/pandas/_libs/parsers.pyx b/pandas/_libs/parsers.pyx
index 7a6f366d5b1a9..2549c8545908d 100644
--- a/pandas/_libs/parsers.pyx
+++ b/pandas/_libs/parsers.pyx
@@ -277,7 +277,7 @@ DEFAULT_CHUNKSIZE = 256 * 1024
 # no longer excluding inf representations
 # '1.#INF','-1.#INF', '1.#INF000000',
 _NA_VALUES = [b'-1.#IND', b'1.#QNAN', b'1.#IND', b'-1.#QNAN',
-              b'#N/A N/A', b'NA', b'#NA', b'NULL', b'null', b'NaN',
+              b'#N/A N/A', b'n/a', b'NA', b'#NA', b'NULL', b'null', b'NaN',
               b'nan', b'']
 
 
diff --git a/pandas/io/common.py b/pandas/io/common.py
index 1c987f6a9dfc3..cbfc33dbebb81 100644
--- a/pandas/io/common.py
+++ b/pandas/io/common.py
@@ -31,7 +31,7 @@
 # '1.#INF','-1.#INF', '1.#INF000000',
 _NA_VALUES = set([
     '-1.#IND', '1.#QNAN', '1.#IND', '-1.#QNAN', '#N/A N/A', '#N/A',
-    'N/A', 'NA', '#NA', 'NULL', 'null', 'NaN', '-NaN', 'nan', '-nan', ''
+    'N/A', 'n/a', 'NA', '#NA', 'NULL', 'null', 'NaN', '-NaN', 'nan', '-nan', ''
 ])
 
 try:
diff --git a/pandas/tests/io/parser/na_values.py b/pandas/tests/io/parser/na_values.py
index 6f72ed51d76c6..170f9d428c9cc 100644
--- a/pandas/tests/io/parser/na_values.py
+++ b/pandas/tests/io/parser/na_values.py
@@ -70,8 +70,8 @@ def test_non_string_na_values(self):
 
     def test_default_na_values(self):
         _NA_VALUES = set(['-1.#IND', '1.#QNAN', '1.#IND', '-1.#QNAN',
-                          '#N/A', 'N/A', 'NA', '#NA', 'NULL', 'null', 'NaN',
-                          'nan', '-NaN', '-nan', '#N/A N/A', ''])
+                          '#N/A', 'N/A', 'n/a', 'NA', '#NA', 'NULL', 'null',
+                          'NaN', 'nan', '-NaN', '-nan', '#N/A N/A', ''])
         assert _NA_VALUES == parsers._NA_VALUES
         nv = len(_NA_VALUES)