diff --git a/CHANGELOG.md b/CHANGELOG.md
index 5df9f6b0..34239b17 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2,6 +2,10 @@
 
 ## Next version
 
+### API changes
+
+- Add `Nullable.isNull`, `Nullable.isUndefined`, and similar functions to `Nullable` and `Null` modules. https://github.com/rescript-association/rescript-core/pull/125
+
 ## 0.4.0
 
 ### API changes
diff --git a/src/Core__Null.mjs b/src/Core__Null.mjs
index d6c6e83b..813069fc 100644
--- a/src/Core__Null.mjs
+++ b/src/Core__Null.mjs
@@ -63,6 +63,10 @@ function flatMap(value, f) {
   }
 }
 
+function isNull(i) {
+  return i === null;
+}
+
 export {
   equal ,
   compare ,
@@ -72,5 +76,6 @@ export {
   map ,
   mapWithDefault ,
   flatMap ,
+  isNull ,
 }
 /* No side effect */
diff --git a/src/Core__Null.res b/src/Core__Null.res
index 023ad78c..74bd38a3 100644
--- a/src/Core__Null.res
+++ b/src/Core__Null.res
@@ -49,3 +49,5 @@ let flatMap = (value, f) =>
   | Some(x) => f(x)
   | None => null
   }
+
+let isNull = i => i == null
diff --git a/src/Core__Null.resi b/src/Core__Null.resi
index f2e917fc..aa70ad74 100644
--- a/src/Core__Null.resi
+++ b/src/Core__Null.resi
@@ -174,3 +174,17 @@ Null.flatMap(null, addIfAboveOne) // null
 ```
 */
 let flatMap: (t<'a>, 'a => t<'b>) => t<'b>
+
+/**
+`isNull(value)` checks if `value===null`
+
+## Examples
+
+```rescript
+"abc"->Null.make->Null.isNull // false
+Nullable.undefined->Null.make->Null.isNull // false
+Null.null->Null.isNull // true
+None->Null.make->Null.isNull // false
+```
+*/
+let isNull: t<'a> => bool
diff --git a/src/Core__Nullable.mjs b/src/Core__Nullable.mjs
index 00606cb3..aee08f94 100644
--- a/src/Core__Nullable.mjs
+++ b/src/Core__Nullable.mjs
@@ -62,6 +62,22 @@ function flatMap(value, f) {
   }
 }
 
+function isNull(i) {
+  return i === null;
+}
+
+function isUndefined(i) {
+  return i === undefined;
+}
+
+function isNullOrUndefined(i) {
+  if (i === undefined) {
+    return true;
+  } else {
+    return i === null;
+  }
+}
+
 export {
   equal ,
   compare ,
@@ -71,5 +87,8 @@ export {
   map ,
   mapWithDefault ,
   flatMap ,
+  isNull ,
+  isUndefined ,
+  isNullOrUndefined ,
 }
 /* No side effect */
diff --git a/src/Core__Nullable.res b/src/Core__Nullable.res
index 51849685..ff047a3f 100644
--- a/src/Core__Nullable.res
+++ b/src/Core__Nullable.res
@@ -49,3 +49,7 @@ let flatMap = (value, f) =>
   | Some(x) => f(x)
   | None => Obj.magic(value)
   }
+
+let isNull = i => i == null
+let isUndefined = i => i == undefined
+let isNullOrUndefined = i => i == undefined || i == null
diff --git a/src/Core__Nullable.resi b/src/Core__Nullable.resi
index 4ca135ac..818fb12d 100644
--- a/src/Core__Nullable.resi
+++ b/src/Core__Nullable.resi
@@ -184,3 +184,45 @@ Nullable.flatMap(Nullable.null, addIfAboveOne) // undefined
 ```
 */
 let flatMap: (t<'a>, 'a => t<'b>) => t<'b>
+
+/**
+`isNull(value)` checks if `value===null`
+
+## Examples
+
+```rescript
+"abc"->Nullable.make->Nullable.isNull // false
+Nullable.undefined->Nullable.isNull // false
+Nullable.null->Nullable.isNull // true
+None->Nullable.make->Nullable.isNull // false
+```
+*/
+let isNull: t<'a> => bool
+
+/**
+`isUndefined(value)` checks if `value===undefined`
+
+## Examples
+
+```rescript
+"abc"->Nullable.make->Nullable.isUndefined // false
+Nullable.null->Nullable.isUndefined // false
+Nullable.undefined->Nullable.isUndefined // true
+None->Nullable.make->Nullable.isUndefined // true
+```
+*/
+let isUndefined: t<'a> => bool
+
+/**
+`isNullOrUndefined(value)` checks if `value===undefined || value===null`
+
+## Examples
+
+```rescript
+"abc"->Nullable.make->Nullable.isNullOrUndefined // false
+Nullable.null->Nullable.isNullOrUndefined // true
+Nullable.undefined->Nullable.isUndefined // true
+None->Nullable.make->Nullable.isNullOrUndefined // true
+```
+*/
+let isNullOrUndefined: t<'a> => bool
diff --git a/test/NullableTests.mjs b/test/NullableTests.mjs
new file mode 100644
index 00000000..26af6602
--- /dev/null
+++ b/test/NullableTests.mjs
@@ -0,0 +1,173 @@
+// Generated by ReScript, PLEASE EDIT WITH CARE
+
+import * as Test from "./Test.mjs";
+import * as Caml_obj from "rescript/lib/es6/caml_obj.js";
+import * as Core__Null from "../src/Core__Null.mjs";
+import * as Core__Nullable from "../src/Core__Nullable.mjs";
+
+var eq = Caml_obj.equal;
+
+Test.run([
+      [
+        "NullableTests.res",
+        7,
+        20,
+        38
+      ],
+      "isNull when null"
+    ], Core__Nullable.isNull(null), eq, true);
+
+Test.run([
+      [
+        "NullableTests.res",
+        8,
+        20,
+        39
+      ],
+      "isNull when undef"
+    ], Core__Nullable.isNull(undefined), eq, false);
+
+Test.run([
+      [
+        "NullableTests.res",
+        9,
+        20,
+        37
+      ],
+      "isNull when abc"
+    ], Core__Nullable.isNull("abc"), eq, false);
+
+Test.run([
+      [
+        "NullableTests.res",
+        10,
+        20,
+        38
+      ],
+      "isNull when None"
+    ], Core__Nullable.isNull(undefined), eq, false);
+
+Test.run([
+      [
+        "NullableTests.res",
+        12,
+        20,
+        39
+      ],
+      "isUndef when null"
+    ], Core__Nullable.isUndefined(null), eq, false);
+
+Test.run([
+      [
+        "NullableTests.res",
+        13,
+        20,
+        40
+      ],
+      "isUndef when undef"
+    ], Core__Nullable.isUndefined(undefined), eq, true);
+
+Test.run([
+      [
+        "NullableTests.res",
+        14,
+        20,
+        38
+      ],
+      "isUndef when abc"
+    ], Core__Nullable.isUndefined("abc"), eq, false);
+
+Test.run([
+      [
+        "NullableTests.res",
+        15,
+        20,
+        39
+      ],
+      "isUndef when None"
+    ], Core__Nullable.isUndefined(undefined), eq, true);
+
+Test.run([
+      [
+        "NullableTests.res",
+        17,
+        20,
+        45
+      ],
+      "isNullOrUndef when null"
+    ], Core__Nullable.isNullOrUndefined(null), eq, true);
+
+Test.run([
+      [
+        "NullableTests.res",
+        19,
+        13,
+        39
+      ],
+      "isNullOrUndef when undef"
+    ], Core__Nullable.isNullOrUndefined(undefined), eq, true);
+
+Test.run([
+      [
+        "NullableTests.res",
+        25,
+        13,
+        37
+      ],
+      "isNullOrUndef when abc"
+    ], Core__Nullable.isNullOrUndefined("abc"), eq, false);
+
+Test.run([
+      [
+        "NullableTests.res",
+        31,
+        13,
+        38
+      ],
+      "isNullOrUndef when None"
+    ], Core__Nullable.isNullOrUndefined(undefined), eq, true);
+
+Test.run([
+      [
+        "NullableTests.res",
+        37,
+        20,
+        56
+      ],
+      "isNull when null using Null module"
+    ], Core__Null.isNull(null), eq, true);
+
+Test.run([
+      [
+        "NullableTests.res",
+        39,
+        13,
+        50
+      ],
+      "isNull when undef using Null module"
+    ], Core__Null.isNull(undefined), eq, false);
+
+Test.run([
+      [
+        "NullableTests.res",
+        44,
+        20,
+        55
+      ],
+      "isNull when abc using Null module"
+    ], Core__Null.isNull("abc"), eq, false);
+
+Test.run([
+      [
+        "NullableTests.res",
+        45,
+        20,
+        56
+      ],
+      "isNull when None using Null module"
+    ], Core__Null.isNull(undefined), eq, false);
+
+export {
+  eq ,
+}
+/*  Not a pure module */
diff --git a/test/NullableTests.res b/test/NullableTests.res
new file mode 100644
index 00000000..4df52769
--- /dev/null
+++ b/test/NullableTests.res
@@ -0,0 +1,45 @@
+open RescriptCore
+
+let eq = (a, b) => a == b
+
+// ===== isNull, isUndefined, isNullOrUndefined =====
+
+Test.run(__POS_OF__("isNull when null"), Nullable.null->Nullable.isNull, eq, true)
+Test.run(__POS_OF__("isNull when undef"), Nullable.undefined->Nullable.isNull, eq, false)
+Test.run(__POS_OF__("isNull when abc"), "abc"->Nullable.make->Nullable.isNull, eq, false)
+Test.run(__POS_OF__("isNull when None"), None->Nullable.make->Nullable.isNull, eq, false)
+
+Test.run(__POS_OF__("isUndef when null"), Nullable.null->Nullable.isUndefined, eq, false)
+Test.run(__POS_OF__("isUndef when undef"), Nullable.undefined->Nullable.isUndefined, eq, true)
+Test.run(__POS_OF__("isUndef when abc"), "abc"->Nullable.make->Nullable.isUndefined, eq, false)
+Test.run(__POS_OF__("isUndef when None"), None->Nullable.make->Nullable.isUndefined, eq, true)
+
+Test.run(__POS_OF__("isNullOrUndef when null"), Nullable.null->Nullable.isNullOrUndefined, eq, true)
+Test.run(
+  __POS_OF__("isNullOrUndef when undef"),
+  Nullable.undefined->Nullable.isNullOrUndefined,
+  eq,
+  true,
+)
+Test.run(
+  __POS_OF__("isNullOrUndef when abc"),
+  "abc"->Nullable.make->Nullable.isNullOrUndefined,
+  eq,
+  false,
+)
+Test.run(
+  __POS_OF__("isNullOrUndef when None"),
+  None->Nullable.make->Nullable.isNullOrUndefined,
+  eq,
+  true,
+)
+
+Test.run(__POS_OF__("isNull when null using Null module"), Null.null->Null.isNull, eq, true)
+Test.run(
+  __POS_OF__("isNull when undef using Null module"),
+  Nullable.undefined->Null.make->Null.isNull,
+  eq,
+  false,
+)
+Test.run(__POS_OF__("isNull when abc using Null module"), "abc"->Null.make->Null.isNull, eq, false)
+Test.run(__POS_OF__("isNull when None using Null module"), None->Null.make->Null.isNull, eq, false)
diff --git a/test/TestSuite.mjs b/test/TestSuite.mjs
index 3d8e7128..42c08b3a 100644
--- a/test/TestSuite.mjs
+++ b/test/TestSuite.mjs
@@ -6,6 +6,7 @@ import * as ArrayTests from "./ArrayTests.mjs";
 import * as ErrorTests from "./ErrorTests.mjs";
 import * as PromiseTest from "./PromiseTest.mjs";
 import * as ResultTests from "./ResultTests.mjs";
+import * as NullableTests from "./NullableTests.mjs";
 import * as TypedArrayTests from "./TypedArrayTests.mjs";
 
 var bign = TestTests.bign;
@@ -34,8 +35,6 @@ var forEachIfOkCallFunction = ResultTests.forEachIfOkCallFunction;
 
 var forEachIfErrorDoNotCallFunction = ResultTests.forEachIfErrorDoNotCallFunction;
 
-var eq = TypedArrayTests.eq;
-
 var num1 = TypedArrayTests.num1;
 
 var num2 = TypedArrayTests.num2;
@@ -50,6 +49,8 @@ var areSame = TypedArrayTests.areSame;
 
 var o = TypedArrayTests.o;
 
+var eq = NullableTests.eq;
+
 export {
   bign ,
   TestError ,
@@ -64,7 +65,6 @@ export {
   $$catch ,
   forEachIfOkCallFunction ,
   forEachIfErrorDoNotCallFunction ,
-  eq ,
   num1 ,
   num2 ,
   num3 ,
@@ -72,5 +72,6 @@ export {
   assertWillThrow ,
   areSame ,
   o ,
+  eq ,
 }
 /* IntTests Not a pure module */
diff --git a/test/TestSuite.res b/test/TestSuite.res
index 18bd6273..07d209ab 100644
--- a/test/TestSuite.res
+++ b/test/TestSuite.res
@@ -5,3 +5,4 @@ include ArrayTests
 include IntTests
 include ResultTests
 include TypedArrayTests
+include NullableTests