diff --git a/docs/content/index.fsx b/docs/content/index.fsx
index 0df15d40..e3a80d34 100644
--- a/docs/content/index.fsx
+++ b/docs/content/index.fsx
@@ -139,6 +139,9 @@ anObj |> should not' (be sameAs otherObj)
 [1..10] |> should be (supersetOf [3;6;9])
 [1..10] |> should not' (be supersetOf [5;11;21])
 
+[3;6;9] |> should be (subsetOf [1..10])
+[5;11;21] |> should not' (be subsetOf [1..10])
+
 (**
 The ofCase operator allows you to check the case of a union.
 Supplying an expression that will result in a non-union type as well as supplying a non-union type as value argument will result in an exception detailing which parameter is wrong. Note that the actual value of the case is NOT checked, e.g. using `<@ MyCase 5 @>` as expression and `(MyCase 10)` as parameter will succeed. It is possible to check for more than one case by using a tuple of union cases.
diff --git a/docs/content/operators.md b/docs/content/operators.md
index 8bd989fa..4e024d71 100644
--- a/docs/content/operators.md
+++ b/docs/content/operators.md
@@ -39,3 +39,4 @@ Operators comparison across frameworks
 | `inRange`              | +     | +     | +      |
 | `ofCase`               | +     | +     | +      |
 | `supersetOf`           | +     | +     | +      |
+| `subsetOf`             | +     | +     | +      |
\ No newline at end of file
diff --git a/src/FsUnit.MsTestUnit/FsUnit.fs b/src/FsUnit.MsTestUnit/FsUnit.fs
index 551c9bf8..d48bbc7c 100644
--- a/src/FsUnit.MsTestUnit/FsUnit.fs
+++ b/src/FsUnit.MsTestUnit/FsUnit.fs
@@ -112,4 +112,6 @@ let inRange min max = CustomMatchers.inRange min max
 
 let ofCase case = CustomMatchers.ofCase case
 
-let supersetOf expected = CustomMatchers.supersetOf expected
\ No newline at end of file
+let supersetOf expected = CustomMatchers.supersetOf expected
+
+let subsetOf expected = CustomMatchers.subsetOf expected
\ No newline at end of file
diff --git a/src/FsUnit.NUnit/FsUnit.fs b/src/FsUnit.NUnit/FsUnit.fs
index 8180f75e..9f911bed 100644
--- a/src/FsUnit.NUnit/FsUnit.fs
+++ b/src/FsUnit.NUnit/FsUnit.fs
@@ -95,4 +95,6 @@ module TopLevelOperators =
 
     let ofCase case = OfSameCaseConstraint(case)
 
-    let supersetOf x = CollectionSupersetConstraint(x)
\ No newline at end of file
+    let supersetOf x = CollectionSupersetConstraint(x)
+
+    let subsetOf x = CollectionSubsetConstraint(x)
\ No newline at end of file
diff --git a/src/FsUnit.Xunit/CustomMatchers.fs b/src/FsUnit.Xunit/CustomMatchers.fs
index dfa095b7..5547446e 100644
--- a/src/FsUnit.Xunit/CustomMatchers.fs
+++ b/src/FsUnit.Xunit/CustomMatchers.fs
@@ -135,6 +135,9 @@ let containf f = CustomMatcher<obj>(sprintf "Contains %s" (f.ToString()),
 let supersetOf x = CustomMatcher<obj>(sprintf "Is superset of %A" x, 
                                 fun c -> Set.isSuperset (Set (unbox c)) (Set x))
 
+let subsetOf x = CustomMatcher<obj>(sprintf "Is subset of %A" x, 
+                                fun c -> Set.isSubset (Set (unbox c)) (Set x))
+
 let matchList xs = CustomMatcher<obj>(sprintf "All elements from list %s" (xs.ToString()),
                           fun ys -> match ys with
                                     | :? list<_> as ys' -> List.sort xs = List.sort ys'
diff --git a/src/FsUnit.Xunit/FsUnit.fs b/src/FsUnit.Xunit/FsUnit.fs
index 732494b9..d5f97c3a 100644
--- a/src/FsUnit.Xunit/FsUnit.fs
+++ b/src/FsUnit.Xunit/FsUnit.fs
@@ -104,4 +104,6 @@ let descending = CustomMatchers.descending
 
 let inRange min max = CustomMatchers.inRange min max
 
-let supersetOf expected = CustomMatchers.supersetOf expected
\ No newline at end of file
+let supersetOf expected = CustomMatchers.supersetOf expected
+
+let subsetOf expected = CustomMatchers.subsetOf expected
\ No newline at end of file
diff --git a/tests/FsUnit.MsTest.Test/Fs30Unit.MsTest.Test.fsproj b/tests/FsUnit.MsTest.Test/Fs30Unit.MsTest.Test.fsproj
index e086c21e..8345515a 100644
--- a/tests/FsUnit.MsTest.Test/Fs30Unit.MsTest.Test.fsproj
+++ b/tests/FsUnit.MsTest.Test/Fs30Unit.MsTest.Test.fsproj
@@ -21,7 +21,8 @@
     <Compile Include="beNullTests.fs" />
     <Compile Include="beOfExactTypeTests.fs" />
     <Compile Include="beSameAsTests.fs" />
-    <Compile Include="beSupersetOf.fs" />
+    <Compile Include="beSupersetOfTests.fs" />
+    <Compile Include="beSubsetOfTests.fs" />
     <Compile Include="beTrueTests.fs" />
     <Compile Include="containTests.fs" />
     <Compile Include="equalTests.fs" />
diff --git a/tests/FsUnit.MsTest.Test/beSubsetOfTests.fs b/tests/FsUnit.MsTest.Test/beSubsetOfTests.fs
new file mode 100644
index 00000000..b257ab11
--- /dev/null
+++ b/tests/FsUnit.MsTest.Test/beSubsetOfTests.fs
@@ -0,0 +1,39 @@
+namespace FsUnit.Test
+open Microsoft.VisualStudio.TestTools.UnitTesting
+open FsUnit.MsTest
+
+[<TestClass>]
+type ``be subsetOf tests`` ()= 
+
+    [<TestMethod>] member test.
+     ``5, 3 and 8 should be subset of 1 to 10`` ()=
+        [5;3;8] |> should be (subsetOf [1..10])
+
+    [<TestMethod>] member test.
+     ``5 should be subset of 1 to 10`` ()=
+        [5] |> should be (subsetOf [1..10])
+
+    [<TestMethod>] member test.
+     ``4 to 8 should be subset of 1 to 10`` ()=
+        {4..8} |> should be (subsetOf {1..10})
+        
+    [<TestMethod>] member test.
+     ``1 to 10 should be subset of 4. 1 and 7`` ()=
+        [|1..10|] |> should be (supersetOf [|4;1;7|])
+
+    [<TestMethod>] member test.
+     ``5, 1 and 11 should not be subset of 1 to 10`` ()=
+        [5;1;11] |> should not' (be subsetOf [|1..10|])
+
+    [<TestMethod>] member test.
+     ``1 to 10 should not be subset of 5`` ()=
+        [1..10] |> should not' (be subsetOf [5])
+
+    [<TestMethod>] member test.
+     ``1 to 10 should be subset of 1 to 10`` ()=
+        [1..10] |> should be (subsetOf [1..10])
+
+    [<TestMethod>] member test.
+     ``should fail on '1 to 11 should be subset of 1 to 10'`` ()=
+        shouldFail (fun () -> 
+            [1..11] |> should be (subsetOf [1..10]))
diff --git a/tests/FsUnit.MsTest.Test/beSupersetOf.fs b/tests/FsUnit.MsTest.Test/beSupersetOfTests.fs
similarity index 89%
rename from tests/FsUnit.MsTest.Test/beSupersetOf.fs
rename to tests/FsUnit.MsTest.Test/beSupersetOfTests.fs
index 9b0c061f..4c1f2dd2 100644
--- a/tests/FsUnit.MsTest.Test/beSupersetOf.fs
+++ b/tests/FsUnit.MsTest.Test/beSupersetOfTests.fs
@@ -34,6 +34,6 @@ type ``be supersetOf tests`` ()=
         [1..10] |> should be (supersetOf [1..10])
 
     [<TestMethod>] member test.
-     ``should fail on '1 to 10 should not be superset of 1 to 10'`` ()=
+     ``should fail on '1 to 10 should be superset of 1 to 11'`` ()=
         shouldFail (fun () -> 
-            [1..10] |> should not' (be supersetOf [1..10]))
+            [1..10] |> should be (supersetOf [1..11]))
diff --git a/tests/FsUnit.NUnit.Test/FsUnit.NUnit.Test.fsproj b/tests/FsUnit.NUnit.Test/FsUnit.NUnit.Test.fsproj
index 3cba3337..005ab162 100644
--- a/tests/FsUnit.NUnit.Test/FsUnit.NUnit.Test.fsproj
+++ b/tests/FsUnit.NUnit.Test/FsUnit.NUnit.Test.fsproj
@@ -13,7 +13,8 @@
     <Compile Include="beEmptyStringTests.fs" />
     <Compile Include="beInRangeTests.fs" />
     <Compile Include="beNullOrEmptyStringTests.fs" />
-    <Compile Include="beSupersetOf.fs" />
+    <Compile Include="beSupersetOfTests.fs" />
+    <Compile Include="beSubsetOfTests.fs" />
     <Compile Include="beTrueTests.fs" />
     <Compile Include="beFalseTests.fs" />
     <Compile Include="beSameAsTests.fs" />
diff --git a/tests/FsUnit.NUnit.Test/beSubsetOfTests.fs b/tests/FsUnit.NUnit.Test/beSubsetOfTests.fs
new file mode 100644
index 00000000..bd5754c7
--- /dev/null
+++ b/tests/FsUnit.NUnit.Test/beSubsetOfTests.fs
@@ -0,0 +1,39 @@
+namespace FsUnit.Test
+open NUnit.Framework
+open FsUnit
+
+[<TestFixture>]
+type ``be subsetOf tests`` ()= 
+
+    [<Test>] member test.
+     ``5, 3 and 8 should be subset of 1 to 10`` ()=
+        [5;3;8] |> should be (subsetOf [1..10])
+
+    [<Test>] member test.
+     ``5 should be subset of 1 to 10`` ()=
+        [5] |> should be (subsetOf [1..10])
+
+    [<Test>] member test.
+     ``4 to 8 should be subset of 1 to 10`` ()=
+        {4..8} |> should be (subsetOf {1..10})
+        
+    [<Test>] member test.
+     ``1 to 10 should be subset of 4. 1 and 7`` ()=
+        [|1..10|] |> should be (supersetOf [|4;1;7|])
+
+    [<Test>] member test.
+     ``5, 1 and 11 should not be subset of 1 to 10`` ()=
+        [5;1;11] |> should not' (be subsetOf [|1..10|])
+
+    [<Test>] member test.
+     ``1 to 10 should not be subset of 5`` ()=
+        [1..10] |> should not' (be subsetOf [5])
+
+    [<Test>] member test.
+     ``1 to 10 should be subset of 1 to 10`` ()=
+        [1..10] |> should be (subsetOf [1..10])
+
+    [<Test>] member test.
+     ``should fail on '1 to 11 should be subset of 1 to 10'`` ()=
+        shouldFail (fun () -> 
+            [1..11] |> should be (subsetOf [1..10]))
\ No newline at end of file
diff --git a/tests/FsUnit.NUnit.Test/beSupersetOf.fs b/tests/FsUnit.NUnit.Test/beSupersetOfTests.fs
similarity index 89%
rename from tests/FsUnit.NUnit.Test/beSupersetOf.fs
rename to tests/FsUnit.NUnit.Test/beSupersetOfTests.fs
index d9197ae7..58f9b2d5 100644
--- a/tests/FsUnit.NUnit.Test/beSupersetOf.fs
+++ b/tests/FsUnit.NUnit.Test/beSupersetOfTests.fs
@@ -34,6 +34,6 @@ type ``be supersetOf tests`` ()=
         [1..10] |> should be (supersetOf [1..10])
 
     [<Test>] member test.
-     ``should fail on '1 to 10 should not be superset of 1 to 10'`` ()=
+     ``should fail on '1 to 10 should be superset of 1 to 11'`` ()=
         shouldFail (fun () -> 
-            [1..10] |> should not' (be supersetOf [1..10]))
+            [1..10] |> should be (supersetOf [1..11]))
diff --git a/tests/FsUnit.Xunit.Test/FsUnit.Xunit.Test.fsproj b/tests/FsUnit.Xunit.Test/FsUnit.Xunit.Test.fsproj
index 39378dc6..06b88d86 100644
--- a/tests/FsUnit.Xunit.Test/FsUnit.Xunit.Test.fsproj
+++ b/tests/FsUnit.Xunit.Test/FsUnit.Xunit.Test.fsproj
@@ -20,7 +20,8 @@
     <Compile Include="beNullTests.fs" />
     <Compile Include="beOfExactTypeTests.fs" />
     <Compile Include="beSameAsTests.fs" />
-    <Compile Include="beSupersetOf.fs" />
+    <Compile Include="beSupersetOfTests.fs" />
+    <Compile Include="beSubsetOfTests.fs" />
     <Compile Include="beTrueTests.fs" />
     <Compile Include="haveCountTests.fs" />
     <Compile Include="haveLengthTests.fs" />
diff --git a/tests/FsUnit.Xunit.Test/beSubsetOfTests.fs b/tests/FsUnit.Xunit.Test/beSubsetOfTests.fs
new file mode 100644
index 00000000..4ab6a7e2
--- /dev/null
+++ b/tests/FsUnit.Xunit.Test/beSubsetOfTests.fs
@@ -0,0 +1,38 @@
+namespace FsUnit.Test
+open Xunit
+open FsUnit.Xunit
+
+type ``be subsetOf tests`` ()= 
+
+    [<Fact>] member test.
+     ``5, 3 and 8 should be subset of 1 to 10`` ()=
+        [5;3;8] |> should be (subsetOf [1..10])
+
+    [<Fact>] member test.
+     ``5 should be subset of 1 to 10`` ()=
+        [5] |> should be (subsetOf [1..10])
+
+    [<Fact>] member test.
+     ``4 to 8 should be subset of 1 to 10`` ()=
+        {4..8} |> should be (subsetOf {1..10})
+        
+    [<Fact>] member test.
+     ``1 to 10 should be subset of 4. 1 and 7`` ()=
+        [|1..10|] |> should be (supersetOf [|4;1;7|])
+
+    [<Fact>] member test.
+     ``5, 1 and 11 should not be subset of 1 to 10`` ()=
+        [5;1;11] |> should not' (be subsetOf [|1..10|])
+
+    [<Fact>] member test.
+     ``1 to 10 should not be subset of 5`` ()=
+        [1..10] |> should not' (be subsetOf [5])
+
+    [<Fact>] member test.
+     ``1 to 10 should be subset of 1 to 10`` ()=
+        [1..10] |> should be (subsetOf [1..10])
+
+    [<Fact>] member test.
+     ``should fail on '1 to 11 should be subset of 1 to 10'`` ()=
+        shouldFail (fun () -> 
+            [1..11] |> should be (subsetOf [1..10]))
diff --git a/tests/FsUnit.Xunit.Test/beSupersetOf.fs b/tests/FsUnit.Xunit.Test/beSupersetOfTests.fs
similarity index 89%
rename from tests/FsUnit.Xunit.Test/beSupersetOf.fs
rename to tests/FsUnit.Xunit.Test/beSupersetOfTests.fs
index 30ced35b..0d37b859 100644
--- a/tests/FsUnit.Xunit.Test/beSupersetOf.fs
+++ b/tests/FsUnit.Xunit.Test/beSupersetOfTests.fs
@@ -33,6 +33,6 @@ type ``be supersetOf tests`` ()=
         [1..10] |> should be (supersetOf [1..10])
 
     [<Fact>] member test.
-     ``should fail on '1 to 10 should not be superset of 1 to 10'`` ()=
+     ``should fail on '1 to 10 should be superset of 1 to 11'`` ()=
         shouldFail (fun () -> 
-            [1..10] |> should not' (be supersetOf [1..10]))
+            [1..10] |> should be (supersetOf [1..11]))